S-4

Large accelerated filer

Accelerated filer

Non-accelerated filer

Smaller reporting company

Emerging growth company

S-4 1 d414067ds4.htm S-4 S-4

As filed with the Securities and Exchange Commission on January 11, 2023

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form S-4

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

PROSPERITY BANCSHARES, INC.

(Exact name of registrant as specified in its charter)


Texas	6022	74-2331986
(State or other jurisdiction of incorporation)	(Primary Standard Industrial Classification Code Number)	(I.R.S. Employer Identification Number)

Prosperity Bank Plaza

4295 San Felipe

Houston, Texas 77027 (281) 269-7199 (Address, including zip code and telephone number, including area code, of registrant’s principal executive offices)

David Zalman

Senior Chairman and Chief Executive Officer Prosperity Bancshares, Inc.

Prosperity Bank Plaza

4295 San Felipe

Houston, Texas 77027

(713) 693-9300

(Name, address, including zip code and telephone number, including area code, of agent for service)

Copies to:

Charlotte M. Rasche

Executive Vice President and General Counsel
80 Sugar Creek Center Blvd.

Sugar Land, Texas 77478

(281) 269-7205

William S. Anderson

Bracewell LLP

711 Louisiana Street, Suite 2300

Houston, Texas 77002

(713) 221-1122

Kenneth L. Burgess, Jr.

President and Chief Executive Officer

First Bancshares of Texas, Inc.

310 West Wall Street, Suite 1200

Midland, Texas 79701

(844) 322-8392

Alan Lackey

President and Chief Executive Officer

Lone Star State Bancshares, Inc.

6220 Milwaukee Avenue

Lubbock, Texas 79424

(806) 771-7717

Chet A. Fenimore

Geoffrey S. Kay

Fenimore Kay Harrison LLP

812 San Antonio Street, Suite 600

Austin, Texas 78701

(512) 583-5900

Approximate date of commencement of proposed sale of the securities to the public: As soon as practicable after this Registration Statement becomes effective and upon completion of the mergers described in the enclosed proxy statement/prospectus.

If the securities being registered on this Form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box. ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer) ☐

Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer) ☐

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this proxy statement/prospectus is not complete and may be changed. Prosperity Bancshares, Inc. may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This document is not an offer to sell these securities, and Prosperity Bancshares, Inc. is not soliciting offers to buy these securities, in any state where the offer or sale is not permitted.

PRELIMINARY—SUBJECT TO COMPLETION—DATED JANUARY 11, 2023

LOGO

MERGER PROPOSED—YOUR VOTE IS VERY IMPORTANT

Dear Shareholders of First Bancshares of Texas, Inc.:

On [ ], 2023 a special meeting of the shareholders of First Bancshares of Texas, Inc., or “First Bancshares,” will be held to vote on a proposal to merge with Prosperity Bancshares, Inc., or “Prosperity,” a Texas corporation and the parent company of Prosperity Bank. On October 10, 2022, Prosperity and First Bancshares entered into an Agreement and Plan of Reorganization, which we refer to as the “First Bancshares reorganization agreement,” that (i) provides for the merger of First Bancshares with and into Prosperity, with Prosperity as the surviving corporation in the merger, which we refer to as the “First Bancshares merger,” and (ii) contemplates that immediately following the First Bancshares merger, the merger of FirstCapital Bank of Texas, National Association, or “FirstCapital Bank,” a wholly owned subsidiary of First Bancshares, with and into Prosperity Bank, with Prosperity Bank as the surviving bank.

If the First Bancshares merger is completed, all shares of First Bancshares common stock issued and outstanding immediately prior to the effective time of the First Bancshares merger will be converted into an aggregate of 3,583,370 shares of Prosperity common stock, which we refer to as the “First Bancshares stock consideration,” and $93,422,648 in cash, which we refer to as the “First Bancshares cash consideration,” and together with the First Bancshares stock consideration, the “First Bancshares merger consideration,” less any amounts paid at closing with respect to outstanding equity awards, as set forth in the First Bancshares reorganization agreement. Additionally, the aggregate First Bancshares cash consideration will be reduced on a dollar-for-dollar basis if First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is less than $204,000,000 at closing of the First Bancshares merger. Because of the possibility of an adjustment to the First Bancshares cash consideration, you will not know the exact amount of cash you will receive in connection with the First Bancshares merger when you vote on the First Bancshares reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each First Bancshares shareholder will receive.

For illustration purposes only, if the First Bancshares merger occurs and assuming at the closing that (i) there are [ ] shares of First Bancshares common stock issued and outstanding, (ii) there are [ ] unexercised options to purchase shares of First Bancshares common stock with a weighted average exercise price of $[ ], (iii) First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is equal to or greater than $204,000,000, and (iv) the price per share of Prosperity common stock received in the First Bancshares merger is equal to $[ ], which was the closing price per share of Prosperity common stock on [ ], 2023, then holders of First Bancshares common stock will receive [ ] shares of Prosperity common stock with a value of $[ ] (prior to adjustments for fractional shares) and $[ ] in cash for each share they own, for an aggregate implied value of $[ ] for each share of First Bancshares common stock.

In addition to the First Bancshares merger, Prosperity and Lone Star State Bancshares, Inc., or “Lone Star,” a Texas corporation and the parent company of Lone Star State Bank of West Texas, or “Lone Star Bank,” a wholly owned subsidiary of Lone Star, have entered into an Agreement and Plan of Reorganization, which we refer to as the “Lone Star reorganization agreement,” that (i) provides for the merger of Lone Star with and into Prosperity, with Prosperity as the surviving corporation in the merger, which we refer to as the “Lone Star merger,” and (ii) contemplates that immediately following the Lone Star merger, the merger of Lone Star Bank with and into Prosperity Bank, with Prosperity Bank as the surviving bank. Lone Star Bank operates five banking offices in the West Texas area, including its main office in Lubbock and one banking center in each of Brownfield, Midland, Odessa and Big Spring, Texas. As of September 30, 2022, Lone Star Bank had total assets of approximately $1.39 billion, gross loans of approximately $940.5 million, total deposits of approximately $1.25 billion, and total shareholders’ equity of approximately $134.2 million.

Neither the closing of the First Bancshares merger nor the closing of the Lone Star merger is conditioned upon closing of the other merger. While the Lone Star shareholders will need to approve the Lone Star merger for it to be consummated, the First Bancshares shareholders will not be required to approve the Lone Star merger. Information included in this proxy statement/prospectus with respect to Lone Star and the Lone Star merger is provided as information for First Bancshares shareholders to consider when voting upon the First Bancshares merger.

If the First Bancshares merger and the Lone Star merger, which we refer to collectively as the “mergers,” are both completed, existing Prosperity shareholders would own approximately [ ]% of Prosperity’s common stock immediately following completion of the mergers, former First Bancshares shareholders would own approximately [ ]% and former Lone Star shareholders would own approximately [ ]%. If the First Bancshares merger is completed but the Lone Star merger is not completed, existing Prosperity shareholders and First Bancshares shareholders would own approximately [ ]% and [ ]%, respectively, of Prosperity’s common stock upon completion of the First Bancshares merger. Prosperity’s common stock is listed on the New York Stock Exchange under the symbol “PB,” and the closing price of Prosperity common stock on [ ], 2023 was $[ ] per share.

First Bancshares will hold a special meeting of its shareholders in a completely virtual format in connection with the First Bancshares merger. Prosperity and First Bancshares cannot complete the First Bancshares merger unless the holders of First Bancshares common stock approve the First Bancshares reorganization agreement and the transactions contemplated thereby, including the First Bancshares merger. First Bancshares’ board of directors, or the “First Bancshares board of directors,” is providing this document to solicit First Bancshares shareholders’ proxy to vote in connection with the proposal to approve the First Bancshares reorganization agreement and related matters. This document is also being delivered to First Bancshares shareholders and Lone Star shareholders as Prosperity’s prospectus for its offering of Prosperity common stock in connection with the mergers.

The First Bancshares special meeting will be held virtually on [ ], 2023, at [ ], Central Time. In order to attend the First Bancshares special meeting, shareholders must register before the special meeting date from a computer, tablet or smartphone by accessing the following web address: [https://fcbtexas.com/FBOTMeeting]. After registering, you will receive a confirmation email containing information about joining the First Bancshares special meeting virtually. There will not be a physical meeting to attend in person.

First Bancshares shareholders, your vote is very important.

To ensure your representation at the First Bancshares special meeting, please complete, sign, date and return the enclosed proxy. Sending in your proxy will not prevent you from voting your shares virtually at the First Bancshares special meeting, since you may revoke your proxy at any time before it is voted. You may revoke your proxy at any time prior to [ ], Central Time, on [ ], 2023 by (i) delivering a written revocation letter to First Bancshares’ transfer agent, Manhattan Transfer Registrar Co., by facsimile at (631) 209-8143 or by email at dcarlo@mtrco.com, (ii) completing, signing, dating and returning a proxy with a later date in accordance with the instructions on the enclosed proxy, or (iii) attending the First Bancshares special meeting virtually and voting your shares of First Bancshares common stock electronically at the First Bancshares special meeting.

The First Bancshares board of directors unanimously approved the First Bancshares reorganization agreement and the transactions contemplated thereby and recommends that First Bancshares shareholders vote “FOR” approval of the First Bancshares reorganization agreement, and, if necessary or appropriate, “FOR” the proposal to adjourn the First Bancshares special meeting to solicit additional proxies in favor of the First Bancshares reorganization agreement.

This document contains a more complete description of the special meeting of First Bancshares, the First Bancshares merger, the Lone Star merger, the documents related to the mergers and other related matters. Please carefully read the entire proxy statement/prospectus, including the “Risk Factors” section, beginning on page 33, for a discussion of the proposed mergers and the risks relating to the proposed mergers. You may also obtain information about Prosperity from documents that Prosperity has filed with the Securities and Exchange Commission. The First Bancshares Board of Directors enthusiastically supports the First Bancshares

merger and recommends that you vote in favor of the approval of the First Bancshares reorganization agreement and the transactions contemplated thereby.

Sincerely,

Kenneth L. Burgess, Jr.

Chairman and Chief Executive Officer

First Bancshares of Texas, Inc.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued under this proxy statement/prospectus or determined if this proxy statement/prospectus is accurate or adequate. Any representation to the contrary is a criminal offense. The securities that Prosperity is offering through this document are not savings or deposit accounts or other obligations of any bank or nonbank subsidiary of Prosperity, First Bancshares or Lone Star, and they are not insured by the Federal Deposit Insurance Corporation or any other governmental agency.

This proxy statement/prospectus is dated [ ], 2023, and it is first being mailed or otherwise delivered to the shareholders of First Bancshares on or about [ ], 2023.

LOGO

MERGER PROPOSED—YOUR VOTE IS VERY IMPORTANT

Dear Shareholders of Lone Star State Bancshares, Inc.:

On [ ], 2023 a special meeting of the shareholders of Lone Star State Bancshares, Inc., or “Lone Star,” will be held to vote on a proposal to merge with Prosperity Bancshares, Inc., or “Prosperity,” a Texas corporation and the parent company of Prosperity Bank. On October 10, 2022, Prosperity and Lone Star entered into an Agreement and Plan of Reorganization, which we refer to as the “Lone Star reorganization agreement,” that (i) provides for the merger of Lone Star with and into Prosperity, with Prosperity as the surviving corporation in the merger, which we refer to as the “Lone Star merger,” and (ii) contemplates that immediately following the Lone Star merger, the merger of Lone Star State Bank of West Texas, or “Lone Star Bank,” a wholly owned subsidiary of Lone Star, with and into Prosperity Bank, with Prosperity Bank as the surviving bank.

If the Lone Star merger is completed, all shares of Lone Star common stock issued and outstanding immediately prior to the effective time of the Lone Star merger will be converted into an aggregate of 2,376,182 shares of Prosperity common stock, which we refer to as the “Lone Star stock consideration,” and $64,053,717 in cash, which we refer to as the “Lone Star cash consideration,” and together with the Lone Star stock consideration, the “Lone Star merger consideration,” less any amounts paid at closing with respect to outstanding equity awards, as set forth in the Lone Star reorganization agreement. Additionally, the aggregate Lone Star cash consideration will be reduced on a dollar-for-dollar basis if Lone Star’s equity capital, as calculated under the Lone Star reorganization agreement, is less than $121,088,508 at closing of the Lone Star merger. Because of the possibility of an adjustment to the Lone Star cash consideration, you will not know the exact amount of cash you will receive in connection with the Lone Star merger when you vote on the Lone Star reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each Lone Star shareholder will receive.

For illustration purposes only, if the Lone Star merger occurs and assuming at the closing that (i) there are [ ] shares of Lone Star common stock issued and outstanding, (ii) there are [ ] unexercised stock options and stock appreciation rights with respect to Lone Star common stock with a weighted average exercise or grant price of $[ ], (iii) Lone Star’s equity capital, as calculated under the Lone Star reorganization agreement, is equal to or greater than $121,088,508, and (iv) the price per share of Prosperity common stock received in the Lone Star merger is equal to $[ ], which was the closing price per share of Prosperity common stock on [ ], 2023, then holders of Lone Star common stock will receive [ ] shares of Prosperity common stock with a value of $[ ] (before adjusting for fractional shares) and $[ ] in cash, for each share they own, for an aggregate implied value of $[ ] for each share of Lone Star common stock.

In addition to the Lone Star merger, Prosperity and First Bancshares of Texas, Inc., or “First Bancshares,” a Texas corporation and the parent company of FirstCapital Bank of Texas, National Association, or “FirstCapital Bank,” a national banking association and wholly owned subsidiary of First Bancshares, have entered into an Agreement and Plan of Reorganization, which we refer to as the “First Bancshares reorganization agreement,” that (i) provides for the merger of First Bancshares with and into Prosperity, with Prosperity as the surviving corporation in the merger, which we refer to as the “First Bancshares merger,” and (ii) contemplates that immediately following the First Bancshares merger, the merger of FirstCapital Bank with and into Prosperity Bank, with Prosperity Bank as the surviving bank. FirstCapital Bank operates 16 full-service banking offices in six different markets in West, North and Central Texas areas, including its main office in Midland, and banking offices in Midland, Lubbock, Amarillo, Wichita Falls, Burkburnett, Byers, Henrietta, Dallas, Horseshoe Bay, Marble Falls and Fredericksburg, Texas. As of September 30, 2022, First Bancshares had, on a consolidated basis, total assets of approximately $2.2 billion, gross loans of approximately $1.6 billion, total deposits of approximately $1.8 billion, and total shareholders’ equity of approximately $276.7 million.

Neither the closing of the Lone Star merger nor the closing of the First Bancshares merger is conditioned upon closing of the other merger. While the First Bancshares shareholders will need to approve the First Bancshares merger for it to be consummated, the Lone Star shareholders will not be required to approve the First Bancshares merger. Information included in this proxy statement/prospectus with respect to First Bancshares and the First Bancshares merger is provided as information for Lone Star shareholders to consider when voting upon the Lone Star merger.

If the First Bancshares merger and the Lone Star merger, which we refer to collectively as the “mergers,” are both completed, existing Prosperity shareholders would own approximately [ ]% of Prosperity’s common stock immediately following completion of the mergers, former Lone Star shareholders would own approximately [ ]% and former First Bancshares shareholders would own approximately [ ]%. If the Lone Star merger is completed but the First Bancshares merger is not completed, existing Prosperity shareholders and Lone Star shareholders would own approximately [ ]% and [ ]%, respectively, of Prosperity’s common stock upon completion of the Lone Star merger. Prosperity’s common stock is listed on the New York Stock Exchange under the symbol “PB,” and the closing price of Prosperity common stock on [ ], 2023 was $[ ] per share.

Lone Star will hold a special meeting of its shareholders in connection with the Lone Star merger. Prosperity and Lone Star cannot complete the Lone Star merger unless the holders of Lone Star common stock approve the Lone Star reorganization agreement and the transactions contemplated thereby, including the Lone Star merger. Lone Star’s board of directors, or the “Lone Star board of directors,” is providing this document to solicit Lone Star shareholders’ proxy to vote in connection with the proposal to approve the Lone Star reorganization agreement and related matters. This document is also being delivered to First Bancshares shareholders and Lone Star shareholders as Prosperity’s prospectus for its offering of Prosperity common stock in connection with the mergers.

The Lone Star special meeting will be held on [ ], 2023, at [ ], Central Time, at 6220 Milwaukee Avenue, Lubbock, Texas 79424.

Lone Star shareholders, your vote is very important.

To ensure your representation at the Lone Star special meeting, please complete, sign, date and return the enclosed proxy. Sending in your proxy will not prevent you from voting your shares personally at the Lone Star special meeting, since you may revoke your proxy at any time before it is voted.

The Lone Star board of directors unanimously approved the Lone Star reorganization agreement and the transactions contemplated thereby and recommends that Lone Star shareholders vote “FOR” approval of the Lone Star reorganization agreement, and, if necessary or appropriate, “FOR” the proposal to adjourn the Lone Star special meeting to solicit additional proxies in favor of the Lone Star reorganization agreement.

This document contains a more complete description of the special meeting of Lone Star, the Lone Star merger, the First Bancshares merger, the documents related to the mergers and other related matters. Please carefully read the entire proxy statement/prospectus, including the “Risk Factors” section, beginning on page 33, for a discussion of the proposed mergers and the risks relating to the proposed mergers. You may also obtain information about Prosperity from documents that Prosperity has filed with the Securities and Exchange Commission. The Lone Star Board of Directors enthusiastically supports the Lone Star merger and recommends that you vote in favor of the approval of the Lone Star reorganization agreement and the transactions contemplated thereby.

Sincerely,

Alan Lackey

President and Chief Executive Officer

Lone Star State Bancshares, Inc.

This proxy statement/prospectus is dated [ ], 2023, and it is first being mailed or otherwise delivered to the shareholders of Lone Star on or about [ ], 2023.

HOW TO OBTAIN ADDITIONAL INFORMATION

This proxy statement/prospectus incorporates important business and financial information about Prosperity from documents filed with the SEC that have not been included in or delivered with this document. This information is described on page 141 under “Where You Can Find More Information.” You can obtain free copies of this information by writing or calling:

Prosperity Bancshares, Inc.

Attention: Investor Relations

Prosperity Bank Plaza

4295 San Felipe

Houston, Texas 77027

(281) 269-7199

To obtain timely delivery of the documents before the special meeting of First Bancshares shareholders, you must request the information by [ ], 2023. To obtain timely delivery of the documents before the special meeting of Lone Star shareholders, you must request the information by [ ], 2023.

PLEASE NOTE

We have not authorized anyone to provide you with any information other than the information included in this document and the documents to which we refer you. If someone provides you with other information, please do not rely on it as being authorized by us.

This proxy statement/prospectus has been prepared as of [ ], 2023 and may not reflect changes in the affairs of First Bancshares, Lone Star or Prosperity since that date.

First Bancshares of Texas, Inc.

310 West Wall Street, Suite 1200

Midland, Texas 79701

(432) 687-9102

NOTICE OF SPECIAL MEETING OF SHAREHOLDERS

A special meeting of shareholders of First Bancshares of Texas, Inc. (“First Bancshares”) will be held virtually on [ ], 2023 at [ ], Central Time (the “First Bancshares special meeting”), for the following purposes:

To consider and vote on the proposal to approve the Agreement and Plan of Reorganization, dated as of October 10, 2022 (as it may be amended from time to time, the “First Bancshares reorganization agreement”), by and between Prosperity Bancshares, Inc. (“Prosperity”) and First Bancshares and the transactions contemplated thereby, including the merger of First Bancshares with and into Prosperity (the “First Bancshares merger”), all on and subject to the terms and conditions contained therein; and

To consider and vote on any proposal to adjourn the First Bancshares special meeting to a later date or dates, if necessary or appropriate, including to solicit additional proxies if there are insufficient votes at the time of such adjournment to approve the First Bancshares reorganization agreement and the transactions contemplated thereby.

Only First Bancshares shareholders of record at the close of business on [ ], 2023 will be entitled to notice of, to attend and to vote at the First Bancshares special meeting.

Shareholders of First Bancshares have the right to dissent from the First Bancshares merger and obtain payment in cash of the appraised fair value of their shares of First Bancshares common stock under applicable provisions of the Texas Business Organizations Code. In order for such a shareholder of First Bancshares to perfect his, her or its right to dissent, the shareholder must file a written objection to the First Bancshares merger with First Bancshares prior to the First Bancshares special meeting, vote against the First Bancshares reorganization agreement and file a written demand with Prosperity within 20 days after completion of the First Bancshares merger for payment of the fair value of the shareholder’s shares of First Bancshares common stock. A copy of the applicable statutory provisions of the Texas Business Organizations Code is included as Appendix I to the accompanying proxy statement/prospectus and a summary of these provisions can be found under the caption “The Mergers—Dissenters’ Rights of Appraisal.”

By Order of the Board of Directors,

Kenneth L. Burgess, Jr.

Chairman and Chief Executive Officer

Midland, Texas

[ ], 2023

The board of directors of First Bancshares unanimously recommends that you vote “FOR” the approval of the First Bancshares reorganization agreement and the transactions contemplated thereby.

Your Vote is Very Important

A proxy card is enclosed. Whether or not you plan to attend the special meeting, please complete, sign and date the proxy card and promptly mail it in the enclosed envelope. You may revoke your proxy card in the manner described in the proxy statement/prospectus at any time before it is exercised. If you attend the special meeting, you may change your vote if you wish, even if you have previously returned your proxy card.

VIRTUAL ACCESS TO THE FIRST BANCSHARES SPECIAL MEETING

In order to attend the First Bancshares special meeting, First Bancshares shareholders must register before the special meeting date from a computer, tablet or smartphone by accessing the following web address: [https://fcbtexas.com/FBOTMeeting].

After registering, you will receive a confirmation email containing information about joining the First Bancshares special meeting virtually. There will not be a physical First Bancshares meeting to attend in person.

•

We suggest that you login to the First Bancshares special meeting 10-15 minutes prior to the [ ], 2023, [ ], Central Time, start of the First Bancshares special meeting, as once the First Bancshares special meeting has begun, access to the First Bancshares special meeting will be locked.

•

An agenda for the First Bancshares special meeting and the rules of conduct for participation in the meeting will be provided electronically during the First Bancshares special meeting.

•

If the device you are using has a built-in microphone you will be able to offer comments or ask questions at the First Bancshares special meeting when recognized by the moderator; otherwise, you will remain in “mute” mode.

Lone Star State Bancshares, Inc.

6220 Milwaukee Avenue

Lubbock, Texas 79424

(806) 771-7717

NOTICE OF SPECIAL MEETING OF SHAREHOLDERS

A special meeting of shareholders of Lone Star State Bancshares, Inc. (“Lone Star”) will be held on [ ], 2023 at [ ], Central Time, at 6220 Milwaukee Avenue, Lubbock, Texas 79424 (the “Lone Star special meeting”), for the following purposes:

To consider and vote on the proposal to approve the Agreement and Plan of Reorganization, dated as of October 10, 2022 (as it may be amended from time to time, the “Lone Star reorganization agreement”), by and between Prosperity Bancshares, Inc. (“Prosperity”) and Lone Star and the transactions contemplated thereby, including the merger of Lone Star with and into Prosperity (the “Lone Star merger”), all on and subject to the terms and conditions contained therein; and

To consider and vote on any proposal to adjourn the Lone Star special meeting to a later date or dates, if necessary or appropriate, including to solicit additional proxies if there are insufficient votes at the time of such adjournment to approve the Lone Star reorganization agreement and the transactions contemplated thereby.

Only Lone Star shareholders of record at the close of business on [ ], 2023 will be entitled to notice of, to attend and to vote at the Lone Star special meeting.

Shareholders of Lone Star have the right to dissent from the Lone Star merger and obtain payment in cash of the appraised fair value of their shares of Lone Star common stock under applicable provisions of the Texas Business Organizations Code. In order for such a shareholder of Lone Star to perfect his, her or its right to dissent, the shareholder must file a written objection to the Lone Star merger with Lone Star prior to the Lone Star special meeting, vote against the Lone Star reorganization agreement and file a written demand with Prosperity within 20 days after completion of the Lone Star merger for payment of the fair value of the shareholder’s shares of Lone Star common stock. A copy of the applicable statutory provisions of the Texas Business Organizations Code is included as Appendix I to the accompanying proxy statement/prospectus and a summary of these provisions can be found under the caption “The Mergers—Dissenters’ Rights of Appraisal.”

By Order of the Board of Directors,

Alan L. Lackey

President and Chief Executive Officer

Lubbock, Texas

[ ], 2023

The board of directors of Lone Star unanimously recommends that you vote “FOR” the approval of the Lone Star reorganization agreement and the transactions contemplated thereby.

Your Vote is Very Important

A proxy card is enclosed. Whether or not you plan to attend the special meeting, please complete, sign and date the proxy card and promptly mail it in the enclosed envelope. You may revoke your proxy card in the manner described in the proxy statement/prospectus at any time before it is exercised. If you attend the special meeting, you may vote in person if you wish, even if you have previously returned your proxy card.

TABLE OF CONTENTS


QUESTIONS AND ANSWERS			1
The Mergers			1
The First Bancshares Special Meeting			6
The Lone Star Special Meeting			8
Voting and Exchanging Shares			9
SUMMARY			14
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS			29
RISK FACTORS			33
THE FIRST BANCSHARES SPECIAL MEETING			39
THE LONE STAR SPECIAL MEETING			43
THE FIRST BANCSHARES MERGER			47
THE LONE STAR MERGER			67
THE MERGERS			85
THE REORGANIZATION AGREEMENTS			89
MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE MERGERS			110
BUSINESS OF FIRST BANCSHARES			115
BUSINESS OF LONE STAR			117
COMPARATIVE STOCK PRICES AND DIVIDENDS			119
DESCRIPTION OF PROSPERITY COMMON STOCK			123
COMPARISON OF RIGHTS OF SHAREHOLDERS OF PROSPERITY AND FIRST BANCSHARES			125
COMPARISON OF RIGHTS OF SHAREHOLDERS OF PROSPERITY AND LONE STAR			130
TEXAS ANTI-TAKEOVER STATUTES			135
SECURITY OWNERSHIP OF FIRST BANCSHARES DIRECTORS, EXECUTIVE OFFICERS AND CERTAIN BENEFICIAL OWNERS OF FIRST BANCSHARES			136
SECURITY OWNERSHIP OF LONE STAR DIRECTORS, EXECUTIVE OFFICERS AND CERTAIN BENEFICIAL OWNERS OF LONE STAR			138
EXPERTS			140
LEGAL MATTERS			140
OTHER MATTERS			140
WHERE YOU CAN FIND MORE INFORMATION			141
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE			143


Appendix A:	Agreement and Plan of Reorganization, dated as of October 10, 2022, by and between Prosperity Bancshares, Inc. and First Bancshares of Texas, Inc.	A-1
Appendix B:	Agreement and Plan of Reorganization, dated as of October 10, 2022, by and between Prosperity Bancshares, Inc. and Lone Star State Bancshares, Inc.	B-1
Appendix C:	Form of Director Support Agreement, by and among Prosperity Bancshares, Inc., First Bancshares of Texas, Inc., FirstCapital Bank of Texas, National Association, and each of the directors of First Bancshares of Texas, Inc. or FirstCapital Bank of Texas, National Association	C-1
Appendix D:	Form of Director Support Agreement, by and among Prosperity Bancshares, Inc., Lone Star State Bancshares, Inc., Lone Star State Bank of West Texas, and each of the directors of Lone Star State Bancshares, Inc. or Lone Star State Bank of West Texas	D-1
Appendix E:	Form of Voting Agreement, by and among Prosperity Bancshares, Inc. and certain shareholders of First Bancshares of Texas, Inc. stock	E-1
Appendix F:	Form of Voting Agreement, by and among Prosperity Bancshares, Inc. and certain shareholders of Lone Star State Bancshares, Inc. stock	F-1
Appendix G:	Opinion of Stephens Inc. (with respect to First Bancshares of Texas, Inc.)	G-1
Appendix H:	Opinion of Stephens Inc. (with respect to Lone Star State Bancshares, Inc.)	H-1
Appendix I:	Provisions of the Texas Business Organizations Code Relating to Dissenters’ Rights	I-1

QUESTIONS AND ANSWERS

The following are some questions that you may have about the mergers, as described below, the First Bancshares special meeting and the Lone Star special meeting, each as described below, and brief answers to those questions. We urge you to read carefully the remainder of this proxy statement/prospectus because the information in this section does not provide all of the information that might be important to you with respect to the mergers, the First Bancshares special meeting or the Lone Star special meeting. Additional important information is also contained in the documents incorporated by reference into this proxy statement/prospectus. See the section entitled “Where You Can Find More Information” beginning on page 141.

Unless the context otherwise requires, references in this proxy statement/prospectus to “Prosperity” refer to Prosperity Bancshares, Inc., a Texas corporation; references to “First Bancshares” refer to First Bancshares of Texas, Inc., a Texas corporation; references to “Lone Star” refer to Lone Star State Bancshares, Inc., a Texas corporation; references to “FirstCapital Bank” refer to FirstCapital Bank of Texas, National Association, a national banking association and wholly owned subsidiary of First Bancshares; references to “Lone Star Bank” refer to Lone Star State Bank of West Texas, a Texas state-chartered bank and wholly owned subsidiary of Lone Star; and references to “we,” “our” and “us” refer to Prosperity, First Bancshares and Lone Star together.

THE MERGERS

Q:	What are the mergers?

Prosperity and First Bancshares have entered into an Agreement and Plan of Reorganization, dated as of October 10, 2022, which we refer to as the “First Bancshares reorganization agreement,” and Prosperity and Lone Star have entered into an Agreement and Plan of Reorganization, dated as of October 10, 2022, which we refer to as the “Lone Star reorganization agreement.” We refer to the First Bancshares reorganization agreement and the Lone Star reorganization agreement collectively as the “reorganization agreements.” Copies of the First Bancshares reorganization agreement and the Lone Star reorganization agreement are attached to this proxy statement/prospectus as Appendix A and Appendix B, respectively.

Under the First Bancshares reorganization agreement, (i) First Bancshares will merge with and into Prosperity, with Prosperity as the surviving corporation, which we refer to as the “First Bancshares merger,” and (ii) immediately following the First Bancshares merger, FirstCapital Bank will merge with and into Prosperity Bank, with Prosperity Bank as the surviving bank, which we refer to as the “FirstCapital Bank merger.” The First Bancshares merger cannot be completed unless, among other things, the holders of First Bancshares common stock approve the First Bancshares reorganization agreement.

Under the Lone Star reorganization agreement, (i) Lone Star will merge with and into Prosperity, with Prosperity as the surviving corporation, which we refer to as the “Lone Star merger,” and together with the First Bancshares merger, the “mergers,” and (ii) immediately following the Lone Star merger, Lone Star Bank will merge with and into Prosperity Bank, with Prosperity Bank as the surviving bank, which we refer to as the “Lone Star Bank merger,” and collectively with the FirstCapital Bank merger, the “bank mergers.” The Lone Star merger cannot be completed unless, among other things, the holders of Lone Star common stock approve the Lone Star reorganization agreement.

Q:	Is the consummation of one merger conditioned on the consummation of the other merger?

No. The First Bancshares merger may be consummated regardless of whether the Lone Star merger is consummated, and the Lone Star merger may be consummated regardless of whether the First Bancshares merger is consummated. However, information regarding the First Bancshares merger may be relevant to Lone Star shareholders, and vice versa, and we encourage shareholders of each of First Bancshares and Lone Star to read this proxy statement/prospectus in its entirety.

Q:	Why am I receiving this proxy statement/prospectus?

We are delivering this document to the shareholders of First Bancshares and Lone Star because it is a proxy statement being used by each of the boards of directors of First Bancshares and Lone Star to solicit the proxies of their respective shareholders in connection with approval of the respective mergers and related matters.

In order to approve the mergers and related matters, First Bancshares and Lone Star have each called a special meeting of their shareholders, which we refer to as the “First Bancshares special meeting” and the “Lone Star special meeting,” respectively. This document serves as a proxy statement for both the First Bancshares special meeting and the Lone Star special meeting, which we refer to collectively as the “special meetings,” and describes the proposals to be presented at the special meetings.

This document is also a prospectus that is being delivered to First Bancshares shareholders and Lone Star shareholders because Prosperity is offering shares of its common stock, par value $1.00 per share, which we refer to as “Prosperity common stock,” to First Bancshares shareholders and Lone Star shareholders as partial consideration for the First Bancshares merger and the Lone Star merger, respectively.

This proxy statement/prospectus contains important information about the mergers and the other proposals being voted on at the respective special meetings. You should read it carefully and in its entirety. The enclosed materials allow you to have your shares voted by proxy without attending your meeting. Your vote is important. We encourage you to submit your proxy as soon as possible.

Q:	What will First Bancshares shareholders receive in the First Bancshares merger?

If the First Bancshares reorganization agreement is approved by the First Bancshares shareholders and the First Bancshares merger is completed, all shares of First Bancshares common stock issued and outstanding immediately prior to the effective time of the First Bancshares merger, which we refer to as the “First Bancshares effective time,” will be converted into an aggregate of 3,583,370 shares of Prosperity common stock, which we refer to as the “First Bancshares stock consideration,” and $93,422,648 in cash, which we refer to as the “First Bancshares cash consideration,” and together with the First Bancshares stock consideration, the “First Bancshares merger consideration,” less any amounts paid at closing with respect to outstanding equity awards, as set forth in the First Bancshares reorganization agreement.

Additionally, the aggregate First Bancshares cash consideration will be reduced on a dollar-for-dollar basis if First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is less than $204,000,000 at closing of the First Bancshares merger. Because of the possibility of an adjustment to the First Bancshares cash consideration, you will not know the exact amount of cash you will receive in connection with the First Bancshares merger when you vote on the First Bancshares reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each First Bancshares shareholder will receive.

For illustration purposes only, if the First Bancshares merger occurs and assuming at the closing that (i) there are [ ] shares of First Bancshares common stock issued and outstanding, (ii) there are [ ] unexercised options to purchase shares of First Bancshares common stock with a weighted average exercise price of $[ ], (iii) First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is equal to or greater than $204,000,000, and (iv) the price per share of Prosperity common stock received in the First Bancshares merger is equal to $[ ], which was the closing price per share of Prosperity common stock on [ ], 2023, then holders of First Bancshares common stock will receive [ ] shares of Prosperity common stock with a value of $[ ] (before adjusting for fractional shares) and $[ ] in cash for each share they own, for an aggregate implied value of $[ ] for each share of First Bancshares common stock.

common stock will receive, in lieu thereof, an amount in cash, rounded up to the nearest whole cent (without interest), determined by multiplying (i) the fraction of a share (rounded to the nearest thousandth when expressed in decimal form) of Prosperity common stock that such First Bancshares shareholder would otherwise be entitled to receive by (ii) the average of the daily volume-weighted price per share of Prosperity common stock for the 20 consecutive trading days on which shares are actually traded on the New York Stock Exchange, or “NYSE,” ending at the close of trading on the fifth trading day prior to the closing date of the First Bancshares merger, which average we refer to as the “First Bancshares/Prosperity average price.”

If the mergers are both completed, existing Prosperity shareholders would own approximately [ ]% of Prosperity’s common stock immediately following completion of the mergers, former First Bancshares shareholders would own approximately [ ]% and former Lone Star shareholders would own approximately [ ]%. If the First Bancshares merger is completed, but the Lone Star merger is not completed, existing Prosperity shareholders and First Bancshares shareholders would own approximately [ ]% and [ ]%, respectively, of Prosperity’s common stock upon completion of the First Bancshares merger.

Q:	What will Lone Star shareholders receive in the Lone Star merger?

If the Lone Star reorganization agreement is approved by the Lone Star shareholders and the Lone Star merger is subsequently completed, all shares of Lone Star common stock issued and outstanding immediately prior to the effective time of the Lone Star merger, which we refer to as the “Lone Star effective time,” will be converted into an aggregate of 2,376,182 shares of Prosperity common stock, which we refer to as the “Lone Star stock consideration,” and $64,053,717 in cash, which we refer to as the “Lone Star cash consideration,” and together with the Lone Star stock consideration, the “Lone Star merger consideration,” less any amounts paid at closing with respect to outstanding equity awards, as set forth in the Lone Star reorganization agreement.

Additionally, the aggregate Lone Star cash consideration will be reduced on a dollar-for-dollar basis if Lone Star’s equity capital, as calculated under the Lone Star reorganization agreement, is less than $121,088,508 at closing of the Lone Star merger. Because of the possibility of an adjustment to the Lone Star cash consideration, you will not know the exact amount of cash you will receive in connection with the Lone Star merger when you vote on the Lone Star reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each Lone Star shareholder will receive.

Prosperity will not issue any fractional shares of Prosperity common stock in the Lone Star merger. Instead, a Lone Star shareholder who would otherwise be entitled to a fractional share of Prosperity common stock will receive, in lieu thereof, an amount in cash, rounded up to the nearest whole cent (without interest), determined by multiplying (i) the fraction of a share (rounded to the nearest thousandth when expressed in decimal form) of Prosperity common stock that such Lone Star shareholder would otherwise be entitled to receive by (ii) the average of the daily volume-weighted price per share of Prosperity common stock for the 20 consecutive full trading days on which shares are actually traded on the NYSE ending at the close of trading on the fifth trading day prior to the closing date of the Lone Star merger, which average we refer to as the “Lone Star/Prosperity average price.”

If the mergers are both completed, existing Prosperity shareholders would own approximately [ ]% of Prosperity common stock immediately following completion of the mergers, former Lone Star shareholders would own approximately [ ]% and former First Bancshares shareholders would own approximately [ ]%. If the Lone Star merger is completed, but the First Bancshares merger is not completed, existing Prosperity shareholders and Lone Star shareholders would own approximately [ ]% and [ ]%, respectively, of Prosperity common stock upon completion of the Lone Star merger.

Q:	Will the value of the merger consideration for the First Bancshares merger or the Lone Star merger change between the date of this proxy statement/prospectus and the effective time of the mergers?

Yes. Any change in the market price of Prosperity common stock prior to the completion of the mergers will affect the value of the merger consideration that First Bancshares shareholders and Lone Star shareholders will receive upon completion of the respective mergers. Additionally, the amount of merger consideration issued and paid per share in the mergers may increase or decrease if the number of shares of First Bancshares common stock or Lone Star common stock, as applicable, outstanding changes after the date hereof, whether due to the exercise of stock options or otherwise.

Q:	What will Prosperity shareholders receive in the mergers?

Holders of Prosperity common stock, or “Prosperity shareholders,” will not receive any merger consideration as a result of the First Bancshares merger or the Lone Star merger and will continue to hold the number of shares of Prosperity common stock that they currently hold. Following the mergers, shares of Prosperity common stock will continue to be traded on the NYSE under the symbol “PB.”

Q:	How will the mergers affect First Bancshares and Lone Star equity awards?

If the First Bancshares merger is completed, each outstanding and unvested First Bancshares stock option will vest and each outstanding First Bancshares stock option will be converted into the right to receive a cash payment equal to the difference between the per award share merger consideration (as defined in the First Bancshares reorganization agreement) and the per share exercise price for each share of First Bancshares common stock subject to such First Bancshares stock option. Payments to holders of First Bancshares stock options will reduce the aggregate cash consideration to be paid to First Bancshares shareholders.

If the Lone Star merger is completed, each outstanding and unvested Lone Star stock option and stock appreciation right will vest and each outstanding Lone Star stock option and stock appreciation right will be converted into the right to receive a cash payment equal to the difference between the per award share merger consideration (as defined in the Lone Star reorganization agreement) and the per share exercise price (in the case of Lone Star stock options) or initial value (in the case of the Lone Star stock appreciation rights) for each share of Lone Star common stock subject to such Lone Star stock option or stock appreciation right. Payments to holders of Lone Star stock options or stock appreciation rights will reduce the aggregate cash consideration to be paid to Lone Star shareholders.

For further information, see the section entitled “The Reorganization Agreements—Treatment of Equity Awards” on page 91.

Q:	When do you expect to complete the mergers?

Each of Prosperity, First Bancshares and Lone Star expect to complete the respective mergers in the first quarter of 2023. However, we cannot assure you of when or if each merger will be completed. First Bancshares and Lone Star must first obtain shareholder approval for their respective mergers, and the parties to the reorganization agreements also must obtain necessary regulatory approvals and satisfy certain other closing conditions. For further information, see the section entitled “The Reorganization Agreements—Conditions to Completion of the Mergers” beginning on page 93.

Q:	Are there any voting agreements with existing First Bancshares shareholders or Lone Star shareholders?

Yes. In connection with entering into the First Bancshares reorganization agreement, each of the directors and certain executive officers of First Bancshares, in their capacities as shareholders, have separately entered into voting agreements, which we refer to collectively as the “First Bancshares voting agreements,” pursuant to which they agreed to vote their beneficially owned shares of First Bancshares common stock in favor of the First Bancshares merger proposal and certain related matters and against alternative transactions. In connection with entering into the Lone Star reorganization agreement, each of the directors and certain executive officers and shareholders of Lone Star, in their capacities as individuals, have separately entered into voting agreements, which we refer to collectively as the “Lone Star voting agreements,” pursuant to which they agreed to vote their beneficially owned shares of Lone Star common stock in favor of the Lone Star merger proposal and certain related matters and against alternative transactions.

As of the First Bancshares record date, shares constituting approximately [ ]% of the First Bancshares common stock entitled to vote at the First Bancshares special meeting are subject to First Bancshares voting agreements; and as of the Lone Star record date, shares constituting approximately [ ]% of the Lone Star common stock entitled to vote at the Lone Star special meeting are subject to Lone Star voting agreements. For further information, see the section entitled “The Reorganization Agreements—Voting Agreements” beginning on page 107.

Q:	Are there risks involved in undertaking the mergers?

A:	Yes. You should read and carefully consider the risk factors set forth in the section entitled “Risk Factors” beginning on page 33 of this proxy statement/prospectus.

Q:	What happens if the mergers are not completed?

If either or both of the mergers are not completed, holders of First Bancshares common stock or Lone Star common stock, as applicable, will not receive any merger consideration for their shares in connection with the applicable merger. Instead, First Bancshares, Lone Star or both, as applicable, will remain an independent company. In addition, if either or both of the reorganization agreements are terminated in certain circumstances, a termination fee may be required to be paid to Prosperity by First Bancshares or Lone Star, as applicable. See the section entitled “The Reorganization Agreements—Termination Fees and Effect of Termination” beginning on page 104 for a discussion of the circumstances under which termination fees will be required to be paid.

Q:	Are First Bancshares shareholders or Lone Star shareholders entitled to dissenters’ rights?

First Bancshares shareholders and Lone Star shareholders who do not vote in favor of the First Bancshares merger proposal or the Lone Star merger proposal, as applicable, and follow certain procedural steps will be entitled to dissenters’ rights under the provisions of Chapter 10, Subchapter H of the Texas Business Organizations Code, or the “TBOC.” For further information, see the section entitled “The Mergers—Dissenters’ Rights of Appraisal” beginning on page 85. In addition, a copy of Chapter 10, Subchapter H of the of the TBOC is attached as Appendix I to this proxy statement/prospectus.

Q:	What are the material U.S. federal income tax consequences of the First Bancshares merger to First Bancshares shareholders and of the Lone Star merger to Lone Star shareholders?

Each of the First Bancshares merger and the Lone Star merger is intended to qualify as “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended, which we refer to as the “Code,” and it is a condition to the respective obligations of Prosperity and First Bancshares, with

respect to the First Bancshares merger, and of Prosperity and Lone Star, with respect to the Lone Star merger, to complete the applicable merger that each receives a legal opinion from its counsel to that effect. Consistent with such treatment, a U.S. holder (as defined in the section entitled “Material U.S. Federal Income Tax Consequences of the Mergers” beginning on page 110) of First Bancshares common stock or Lone Star common stock will not recognize gain or loss for U.S. federal income tax purposes upon the exchange of their shares of First Bancshares common stock or Lone Star common stock, as applicable, for shares of Prosperity common stock, except that a U.S. holder generally will recognize gain (but not loss) in an amount equal the lesser of (a) the cash consideration received (excluding cash received in lieu of a fractional share) and (b) the gain realized. The amount of gain realized by a U.S. holder will be equal to the amount by which the cash (excluding cashed received in lieu of fractional shares) plus the fair market value, at the effective time of the applicable merger, of the Prosperity common stock received exceeds the holder’s adjusted tax basis in the First Bancshares common stock or Lone Star common stock, as applicable, to be surrendered in exchange therefor.

For further information, see the section entitled “Material U.S. Federal Income Tax Consequences of the Mergers” beginning on page 110. The tax consequences to a U.S. holder of First Bancshares common stock or Lone Star common stock, as applicable, will depend on his, her or its own particular circumstances. In addition, you may be subject to state, local or non-U.S. tax laws that are not discussed in this proxy statement/prospectus. Accordingly, we strongly urge holders of First Bancshares common stock and Lone Star common stock to consult their own tax advisors for a full understanding of the particular tax

Q:	Where can I find more information about Prosperity, First Bancshares and Lone Star?

A:	You can find more information about Prosperity, First Bancshares and Lone Star from the various sources described in the section entitled “Where You Can Find More Information” beginning on page 141.

THE FIRST BANCSHARES SPECIAL MEETING

Q:	What are First Bancshares shareholders being asked to vote on?

First Bancshares is soliciting proxies from its shareholders with respect to (i) a proposal to approve the First Bancshares reorganization agreement, a copy of which is attached as Appendix A to this proxy statement/prospectus, and the transactions contemplated thereby, including the First Bancshares merger, which we refer to as the “First Bancshares merger proposal,” and (ii) a proposal to adjourn the First Bancshares special meeting, if necessary or appropriate, to solicit additional proxies in favor of the First Bancshares merger proposal, which we refer to as the “First Bancshares adjournment proposal.”

Shareholder approval of the First Bancshares merger proposal is required to complete the First Bancshares merger. Completion of the First Bancshares merger is not conditioned upon approval of the First Bancshares adjournment proposal. First Bancshares expects that the First Bancshares adjournment proposal will not be brought before the First Bancshares special meeting if there are sufficient votes to approve the First Bancshares merger proposal. First Bancshares will transact no other business at the First Bancshares special meeting.

Q:	How does the First Bancshares board of directors recommend that First Bancshares shareholders vote at the First Bancshares special meeting?

A:	The First Bancshares board of directors unanimously recommends that First Bancshares shareholders vote “FOR” the First Bancshares merger proposal and, if necessary or appropriate, “FOR” the First Bancshares adjournment proposal.

Q:	When is the First Bancshares special meeting?

A:	The First Bancshares special meeting will be held virtually on [ ], 2023, at [ ], Central Time.

Q:	How can I attend the First Bancshares special meeting?

In order to attend the First Bancshares special meeting, please register before the special meeting date from your computer, tablet or smartphone by accessing the following link: [https://fcbtexas.com/FBOTMeeting]. After registering, you will receive a confirmation email containing information about joining the First Bancshares special meeting virtually. There will not be a physical meeting to attend in person.

Q:	Will I be able to ask questions and vote at the First Bancshares special meeting?

Yes, First Bancshares shareholders that attend the First Bancshares special meeting virtually will be able to ask questions during the meeting. Additionally, a fillable form will be provided online at the beginning of the First Bancshares special meeting for First Bancshares shareholders to vote during the meeting, which will supersede any previously submitted proxy.

Q:	What constitutes a quorum for the First Bancshares special meeting?

The presence at the First Bancshares special meeting, in person or by proxy, of holders of a majority of the outstanding shares of First Bancshares common stock entitled to vote at the First Bancshares special meeting will constitute a quorum. Participation in the First Bancshares special meeting by electronic means in accordance with the instructions given above will constitute the presence in person at the First Bancshares special meeting, except where such shareholder participates in the meeting for the express purpose of objecting to the transaction of business on the ground that the meeting is not lawfully called or convened.

Q:	Who is entitled to vote at the First Bancshares special meeting?

Holders of record of First Bancshares common stock at the close of business on [ ], 2023, which is the date that the First Bancshares board of directors has fixed as the record date for the First Bancshares special meeting, which we refer to as the “First Bancshares record date,” will be entitled to vote at the First Bancshares special meeting.

Q:	What is the vote required to approve each proposal at the First Bancshares special meeting?

A:	*First Bancshares merger proposal:*

Standard: Approval of the First Bancshares merger proposal requires the affirmative vote of holders of at least two-thirds of the outstanding shares of First Bancshares common stock entitled to vote on the proposal. As of the First Bancshares record date, there were [ ] shares of First Bancshares common stock outstanding and entitled to vote at the First Bancshares special meeting. As of the First Bancshares record date, the directors and executive officers of First Bancshares and their affiliates beneficially owned and were entitled to vote approximately [ ] shares of First Bancshares common stock, representing approximately [ ]% of the shares of First Bancshares common stock outstanding on that date.

Effect of abstentions and broker non-votes: If you are a First Bancshares shareholder and mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the First Bancshares special meeting, or if you fail to instruct your bank, broker or other nominee how to vote with respect to the First Bancshares merger proposal, it will have the same effect as a vote against the proposal.

First Bancshares adjournment proposal:

Standard: Approval of the First Bancshares adjournment proposal requires the affirmative vote of holders of at least a majority of the outstanding shares of First Bancshares common stock entitled to vote on the

proposal who are present in person or represented by proxy at the First Bancshares special meeting. A quorum is not required for a vote on the First Bancshares adjournment proposal.

Effect of abstentions and broker non-votes: If you are a First Bancshares shareholder who is present in person or represented by proxy at the First Bancshares special meeting and you mark “ABSTAIN” on your proxy, fail to vote on the First Bancshares adjournment proposal or fail to instruct your bank, broker or other nominee how to vote with respect to the First Bancshares adjournment proposal, it will have the same effect as a vote against the proposal. If you are not present in person or represented by proxy at the First Bancshares special meeting, it will have no effect on the First Bancshares adjournment proposal.

THE LONE STAR SPECIAL MEETING

Q:	What are Lone Star shareholders being asked to vote on?

Lone Star is soliciting proxies from its shareholders with respect to (i) a proposal to approve the Lone Star reorganization agreement, a copy of which is attached as Appendix B to this proxy statement/prospectus, and the transactions contemplated thereby, including the Lone Star merger, which we refer to as the “Lone Star merger proposal,” and (ii) a proposal to adjourn the Lone Star special meeting, if necessary or appropriate, to solicit additional proxies in favor of the Lone Star merger proposal, which we refer to as the “Lone Star adjournment proposal.”

Shareholder approval of the Lone Star merger proposal is required to complete the Lone Star merger. Completion of the Lone Star merger is not conditioned upon approval of the Lone Star adjournment proposal. Lone Star expects that the Lone Star adjournment proposal will not be brought before the Lone Star special meeting if there are sufficient votes to approve the Lone Star merger proposal. Lone Star will transact no other business at the Lone Star special meeting.

Q:	How does the Lone Star board of directors recommend that Lone Star shareholders vote at the Lone Star special meeting?

A:	The Lone Star board of directors unanimously recommends that Lone Star shareholders vote “FOR” the Lone Star merger proposal and, if necessary or appropriate, “FOR” the Lone Star adjournment proposal.

Q:	When and where is the Lone Star special meeting?

A:	The Lone Star special meeting will be held on [ ], 2023, at [ ], Central Time, at 6220 Milwaukee Avenue, Lubbock, Texas 79424.

Q:	What constitutes a quorum for the Lone Star special meeting?

A:	The presence at the Lone Star special meeting, in person or by proxy, of holders of a majority of the shares of Lone Star common stock issued, outstanding and entitled to vote at the Lone Star special meeting will constitute a quorum.

Q:	Who is entitled to vote at the Lone Star special meeting?

Holders of record of Lone Star common stock at the close of business on [ ], 2023, which is the date that the Lone Star board of directors has fixed as the record date for the Lone Star special meeting, which we refer to as the “Lone Star record date,” will be entitled to vote at the Lone Star special meeting.

Q:	What is the vote required to approve each proposal at the Lone Star special meeting?

A:	*Lone Star merger proposal:*

Standard: Approval of the Lone Star merger proposal requires the affirmative vote of holders of at least two-thirds of the outstanding shares of Lone Star common stock entitled to vote on the proposal. As of the Lone Star record date, there were [ ] shares of Lone Star common stock outstanding and entitled to vote at the Lone Star special meeting. As of the Lone Star record date, the directors and executive officers of Lone Star and their affiliates beneficially owned and were entitled to vote approximately [ ] shares of Lone Star common stock, representing approximately [ ]% of the shares of Lone Star common stock outstanding on that date.

Effect of abstentions and broker non-votes: If you are a Lone Star shareholder and mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the Lone Star special meeting, or if you fail to instruct your bank, broker or other nominee how to vote with respect to the Lone Star merger proposal, it will have the same effect as a vote against the proposal.

Lone Star adjournment proposal:

Standard: Approval of the Lone Star adjournment proposal requires the affirmative vote of holders of at least a majority of the outstanding shares of Lone Star common stock entitled to vote on the proposal who are present or represented by proxy at the Lone Star special meeting. A quorum is not required for a vote on the Lone Star adjournment proposal.

Effect of abstentions and broker non-votes: If you are a Lone Star shareholder who is present in person or represented by proxy at the Lone Star special meeting and you mark “ABSTAIN” on your proxy, fail to vote on the Lone Star adjournment proposal or fail to instruct your bank, broker or other nominee how to vote with respect to the Lone Star adjournment proposal, it will have the same effect as a vote against the proposal. If you are not present in person or represented by proxy at the Lone Star special meeting, it will have no effect on the Lone Star adjournment proposal.

VOTING AND EXCHANGING SHARES

Q:	Why is my vote important?

If you do not vote, it will be more difficult for First Bancshares or Lone Star to obtain the necessary quorum to hold their respective special meetings. In addition, each proposal must be approved by the voting requirements described above. The First Bancshares board of directors and the Lone Star board of directors unanimously recommend that you vote “FOR” the First Bancshares merger proposal and “FOR” the Lone Star merger proposal, respectively.

Q:	How many votes do I have?

A:	Each holder of shares of First Bancshares common stock outstanding on the First Bancshares record date, and each holder of shares of Lone Star common stock outstanding on the Lone Star record date, will be entitled to one vote for each share held of record.

Q:	What do I need to do now?

After carefully reading and considering the information contained in this proxy statement/prospectus, including any documents incorporated into this proxy statement/prospectus by reference, and its appendices, First Bancshares shareholders and Lone Star shareholders should complete, sign, date and return the applicable enclosed proxy and return it in the enclosed envelope as soon as possible so that your shares of First Bancshares common stock or Lone Star common stock, as applicable, will be represented at the First Bancshares special meeting or the Lone Star special meeting, respectively.

Please follow the instructions set forth on the applicable proxy or on the voting instruction form provided by the record holder if your shares are held in “street name” by a bank, broker or other nominee.

First Bancshares shareholders that desire to attend the First Bancshares special meeting should register as soon as possible, but before the First Bancshares special meeting date, from a computer, tablet or smartphone by accessing the following web address: [https://fcbtexas.com/FBOTMeeting]. There will not be a physical meeting of the First Bancshares shareholders to attend in person.

Q:	How do I vote?

A:	If you hold your shares of First Bancshares common stock or Lone Star common stock in your name as a shareholder of record, you may use one of the following methods to submit a proxy:

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by mail by completing, signing, dating and returning the applicable proxy in the enclosed envelope, which requires no additional postage if mailed in the United States; or

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in person at the First Bancshares special meeting or Lone Star special meeting.

In order to attend the First Bancshares special meeting and vote in person at the First Bancshares special meeting, please register before the First Bancshares special meeting date from your computer, tablet or smartphone by accessing the following link: [https://fcbtexas.com/FBOTMeeting]. After registering, you will receive a confirmation email containing information about joining the First Bancshares special meeting virtually. A fillable form will be provided online at the beginning of the First Bancshares special meeting for First Bancshares shareholders to vote during the meeting, which will supersede any previously submitted proxy.

Shares held in “street name.” If your shares are held in “street name” by a bank, broker or other nominee, that institution will send you separate instructions describing the procedure for voting your shares. You may not vote shares held in “street name” by returning a proxy directly to First Bancshares or Lone Star, as applicable, or by voting at the First Bancshares special meeting or Lone Star special meeting, as applicable, unless you provide a “legal proxy,” which you must obtain from your bank, broker or other nominee.

Q:	If my shares of common stock are held in “street name” by my bank, broker or other nominee, will my bank, broker or other nominee automatically vote my shares for me?

No. If your shares of First Bancshares common stock or Lone Star common stock are held in “street name” by a bank, broker or other nominee, you must provide the record holder of your shares with instructions on how to vote your shares. Please follow the voting instructions provided by your bank, broker or other nominee. Please note that you may not vote shares held in “street name” by returning a proxy directly to First Bancshares or Lone Star, as applicable, or by voting at the First Bancshares special meeting or Lone Star special meeting, as applicable, unless you provide a “legal proxy,” which you must obtain from your bank, broker or other nominee.

Banks, brokers and other nominees who hold shares of First Bancshares common stock or Lone Star common stock in “street name” for a beneficial owner of those shares typically have the authority to vote in their discretion on “routine” proposals when they have not received instructions from beneficial owners. However, banks, brokers and other nominees are not allowed to exercise voting discretion with respect to the approval of matters determined to be “non-routine,” without specific instructions from the beneficial owner. First Bancshares and Lone Star expect that all proposals to be voted on at the special meetings will be “non-routine” matters. Broker non-votes are shares held by a bank, broker or other nominee with respect to which such entity is not instructed by the beneficial owner of such shares to vote on the particular proposal and the broker does not have discretionary voting power on such proposal.

If you are a First Bancshares shareholder or Lone Star shareholder and you do not instruct your bank, broker or other nominee on how to vote your shares:

•

your bank, broker or other nominee may not vote your shares on the First Bancshares merger proposal or the Lone Star merger proposal, as applicable, which broker non-votes will have the same effect as a vote against such proposal; and

•

your bank, broker or other nominee may not vote your shares on the First Bancshares adjournment proposal or the Lone Star adjournment proposal, as applicable, which broker non-votes will have no effect on such proposal, unless such broker non-votes are considered present for purposes of the First Bancshares special meeting.

Q:	What if I abstain or do not vote?

A:	For purposes of the special meetings, an abstention occurs when a shareholder attends a special meeting, either in person or represented by proxy, but abstains from voting on one or more proposals.

With respect to the First Bancshares merger proposal or the Lone Star merger proposal, if you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the applicable special meeting, or if you fail to instruct your bank, broker or other nominee how to vote, it will have the same effect as a vote against the applicable merger proposal.

If you are a First Bancshares or Lone Star shareholder who is present in person or represented by proxy at your respective special meeting and you mark “ABSTAIN” on your proxy, fail to vote on the relevant adjournment proposal or fail to instruct your bank, broker or other nominee how to vote with respect to the relevant adjournment proposal, it will have the same effect as a vote against the proposal. If you are not present in person or represented by proxy at the applicable special meeting, it will have no effect on the relevant adjournment proposal.

Q:	What will happen if I return my proxy without indicating how to vote?

A:	If any proxy is returned without indication as to how to vote, the shares will be voted in accordance with the recommendations of the board of directors of First Bancshares or Lone Star, as applicable.

Q:	Can I attend the First Bancshares special meeting or the Lone Star special meeting and vote my shares in person?

Yes. All shareholders of First Bancshares and Lone Star, including shareholders of record and shareholders who hold their shares through banks, brokers, nominees or any other holder of record, are invited to attend their respective special meeting. Holders of record of First Bancshares common stock and Lone Star common stock can vote in person at the First Bancshares special meeting and Lone Star special meeting, respectively. If you are not a shareholder of record, you must obtain a proxy, executed in your favor, from the record holder of your shares, such as a broker, bank or other nominee, to be able to vote in person at the applicable special meeting.

Q:	May I change my vote after I have delivered my proxy?

A:	Yes. You may change your vote at any time before your proxy is voted at the First Bancshares special meeting or the Lone Star special meeting, as applicable. You may do so in one of three ways:

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by completing, signing, dating and returning a proxy with a later date in accordance with the instructions on the enclosed proxy;

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by delivering a written revocation letter to First Bancshares’ transfer agent, Manhattan Transfer Registrar Co., by facsimile at (631) 209-8143 or by email at dcarlo@mtrco.com, or to LaNell Martindale at Lone Star at (806) 771-7717 or by email at lmartindale@lonestarwtx.com, as applicable; or

•

by voting in person at the applicable special meeting.

If your shares are held in “street name” by a bank, broker or other nominee, you should follow the instructions of your bank, broker or other nominee regarding the revocation of voting instructions.

Q:	If I am a First Bancshares shareholder or a Lone Star shareholder, should I send in my First Bancshares or Lone Star stock certificates now?

No. You SHOULD NOT send in any stock certificates now. As soon as practicable after the effective time of the applicable merger, you will receive a letter and instructions from Computershare Investor Services, Prosperity’s exchange agent, with respect to the procedures for surrendering your stock certificates in exchange for cash and shares of Prosperity common stock. You must carefully review and complete these materials and return them as instructed along with your stock certificates to receive the merger consideration.

Q:	Whom may I contact if I cannot locate my stock certificate(s)?

A:	First Bancshares shareholders: If you are unable to locate your original First Bancshares stock certificate(s), you should contact Robin Richey, telephone: (432) 687-9102, email: rrichey@fcbtexas.com.

Lone Star shareholders: If you are unable to locate your original Lone Star stock certificate(s), you should contact LaNell Martindale, telephone: (806) 771-7717, email: lmartindale@lonestarwtx.com.

Q:	What should I do if I receive more than one set of voting materials?

First Bancshares shareholders and Lone Star shareholders may receive more than one set of voting materials, including multiple copies of this proxy statement/prospectus and multiple proxies or voting instruction cards. For example, if you hold shares of First Bancshares common stock or Lone Star common stock in more than one brokerage account, you will receive a separate voting instruction card for each brokerage account in which you hold such shares. If you are a holder of record of First Bancshares common stock or Lone Star common stock and your shares are registered in more than one name, you will receive more than one proxy. In addition, if you are a holder of both First Bancshares common stock and Lone Star common stock, you will receive one or more separate proxies or voting instruction cards for each company. Please complete, sign, date and return each proxy and voting instruction card that you receive or otherwise follow the voting instructions set forth in this proxy statement/prospectus to ensure that you vote every share of First Bancshares common stock and/or Lone Star common stock that you own.

Q:	What happens if I sell my shares of First Bancshares common stock or Lone Star common stock after the applicable record date but before the applicable special meeting?

The First Bancshares record date and the Lone Star record date are earlier than the date of the First Bancshares special meeting and the Lone Star special meeting, respectively, and earlier than the date that the mergers are expected to be completed. If you transfer your shares of First Bancshares common stock or Lone Star common stock after the applicable record date but before the date of the applicable special meeting, you will retain your right to vote at such special meeting (provided that such shares remain outstanding on the date of such special meeting), but you will not have the right to receive any applicable merger consideration for the transferred shares of First Bancshares common stock or Lone Star common stock. You will only be entitled to receive the applicable merger consideration in respect of shares of First Bancshares common stock or Lone Star common stock, as applicable, that you hold at the First Bancshares effective time or the Lone Star effective time, respectively.

Q:	Whom should I call with questions?

A:	First Bancshares shareholders: If you need assistance in completing your proxy, have questions regarding the First Bancshares special meeting, or would like additional copies of this proxy statement/prospectus, please contact Robin Richey, telephone: (432) 687-9102, email: rrichey@fcbtexas.com.

Lone Star shareholders: If you need assistance in completing your proxy, have questions regarding the Lone Star special meeting, or would like additional copies of this proxy statement/prospectus, please contact Alan Lackey, telephone: (806) 771-7717, email: alanlackey@lonestarwtx.com, or Melisa Roberts, telephone: (806) 771-7717, email: mroberts@lonestarwtx.com.

SUMMARY

The following summary highlights selected information in this proxy statement/prospectus and may not contain all the information that may be important to you. You should read carefully this entire proxy statement/prospectus, including any document incorporated by reference into this proxy statement/prospectus, and its Appendixes, because this section may not contain all of the information that may be important to you in determining how to vote. For a description of, and instructions as to how to obtain, this information, see the section entitled “Where You Can Find More Information” beginning on page 141. Each item in this summary refers to the page of this proxy statement/prospectus on which that subject is discussed in more detail.

The Companies

Prosperity Bancshares, Inc.

Prosperity Bancshares, Inc.^® was formed in 1983 as a vehicle to acquire the former Allied Bank in Edna, Texas, which was chartered in 1949 as The First National Bank of Edna and is now known as Prosperity Bank. Prosperity is a Texas corporation and registered financial holding company that derives substantially all of its revenues and income from the operation of its bank subsidiary, Prosperity Bank^®. Prosperity Bank provides a wide array of financial products and services to small and medium-sized businesses and consumers. As of September 30, 2022, Prosperity Bank operated 272 full-service banking locations: 65 in the Houston area, including The Woodlands; 30 in the South Texas area including Corpus Christi and Victoria; 62 in the Dallas/Fort Worth area; 22 in the East Texas area; 29 in the Central Texas area including Austin and San Antonio; 34 in the West Texas area including Lubbock, Midland-Odessa and Abilene; 16 in the Bryan/College Station area; 6 in the Central Oklahoma area; and 8 in the Tulsa, Oklahoma area. Prosperity’s common stock is traded on the NYSE under the symbol “PB.”

First Bancshares of Texas, Inc.

First Bancshares of Texas, Inc. is a registered bank holding company with respect to FirstCapital Bank of Texas, National Association, a national banking association. FirstCapital Bank operates 16 full-service banking offices in six different markets in West, North and Central Texas areas, including its main office in Midland, and banking offices in Midland, Lubbock, Amarillo, Wichita Falls, Burkburnett, Byers, Henrietta, Dallas, Horseshoe Bay, Marble Falls and Fredericksburg, Texas. As of September 30, 2022, First Bancshares had, on a consolidated basis, total assets of approximately $2.2 billion, gross loans of approximately $1.6 billion, total deposits of approximately $1.8 billion, and total shareholders’ equity of approximately $276.7 million.

Lone Star State Bancshares, Inc.

Lone Star State Bancshares, Inc. is a registered bank holding company with respect to Lone Star State Bank of West Texas, a Texas banking association. Lone Star Bank operates five banking offices in the West Texas area, including its main office in Lubbock and one banking center in each of Brownfield, Midland, Odessa and Big Spring, Texas. As of September 30, 2022, Lone Star Bank had total assets of approximately $1.39 billion, gross loans of approximately $940.5 million, total deposits of approximately $1.25 billion, and total shareholders’ equity of approximately $134.2 million.

The First Bancshares Merger (page 47)

Proposed Merger of First Bancshares into Prosperity (page 47)

Under the terms and subject to the conditions of the First Bancshares reorganization agreement, among other things, First Bancshares will merge with and into Prosperity, with Prosperity as the surviving corporation in the First Bancshares merger. Immediately following the First Bancshares merger, FirstCapital Bank will merge with and into Prosperity Bank, with Prosperity Bank as the surviving bank.

Terms of the First Bancshares Merger (page 47)

The terms and conditions of the First Bancshares merger are contained in the First Bancshares reorganization agreement, which is attached to this proxy statement/prospectus as Appendix A. We urge you to read the First Bancshares reorganization agreement carefully and in its entirety, as it is the legal document governing the First Bancshares merger. All descriptions in this summary and elsewhere in this proxy statement/prospectus of the terms and conditions of the First Bancshares merger are subject to, and qualified in their entirety by reference to, the First Bancshares reorganization agreement.

First Bancshares Merger Consideration (page 90)

If the First Bancshares reorganization agreement is approved by the First Bancshares shareholders and the First Bancshares merger is completed, all shares of First Bancshares common stock issued and outstanding immediately prior to the First Bancshares effective time will be converted into an aggregate of 3,583,370 shares of Prosperity common stock and $93,422,648 in cash, less any amounts paid at closing with respect to outstanding equity awards, as set forth in the First Bancshares reorganization agreement. Additionally, the aggregate First Bancshares cash consideration will be reduced on a dollar-for-dollar basis if First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is less than $204,000,000 at closing of the First Bancshares merger. Because of the possibility of an adjustment to the First Bancshares cash consideration, you will not know the exact amount of cash you will receive in connection with the First Bancshares merger when you vote on the First Bancshares reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each First Bancshares shareholder will receive.

For illustration purposes only, if the First Bancshares merger occurs and assuming (i) there are [ ] shares of First Bancshares common stock issued and outstanding at the closing of the First Bancshares merger, (ii) there are [ ] unexercised options to purchase shares of First Bancshares common stock with a weighted average exercise price of $[ ] at the closing of the First Bancshares merger, (iii) First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is equal to or greater than $204,000,000 at the closing of the First Bancshares merger, and (iv) the price per share of Prosperity common stock received in the First Bancshares merger is equal to $[ ], which was the closing price per share of Prosperity common stock on [ ], 2023, then holders of First Bancshares common stock will receive [ ] shares of Prosperity common stock with a value of $[ ] (before adjusting for fractional shares) and $[ ] in cash for each share they own, for an aggregate implied value of $[ ] for each share of First Bancshares common stock.

Prosperity will not issue any fractional shares of Prosperity common stock in the First Bancshares merger. Instead, a First Bancshares shareholder who would otherwise be entitled to a fractional share of Prosperity common stock will receive, in lieu thereof, an amount in cash, rounded up to the nearest whole cent (without interest), determined by multiplying (i) the fraction of a share (rounded to the nearest thousandth when expressed in decimal form) of Prosperity common stock that such First Bancshares shareholder would otherwise be entitled to receive by (ii) the First Bancshares/Prosperity average price.

Treatment of Equity Awards—First Bancshares Stock Options (page 91)

each share of First Bancshares common stock subject to such First Bancshares stock option. Payments to holders of First Bancshares stock options will reduce the aggregate cash consideration to be paid to First Bancshares shareholders.

First Bancshares’ Reasons for the First Bancshares Merger and Recommendation of the First Bancshares Board of Directors (page 51)

Based on the reasons discussed elsewhere in this proxy statement/prospectus, the First Bancshares board of directors believes that the First Bancshares merger is in the best interests of First Bancshares and the shareholders of First Bancshares and recommends that First Bancshares shareholders vote “FOR” the First Bancshares merger proposal and “FOR” the First Bancshares adjournment proposal. For a discussion of the circumstances surrounding the First Bancshares merger and the factors considered by the First Bancshares board of directors in approving the First Bancshares reorganization agreement, see the discussion beginning on page 51.

Opinion of First Bancshares’ Financial Advisor (page 54; Appendix G)

At the meeting of the First Bancshares board of directors on October 10, 2022, Lone Star’s financial advisor, Stephens Inc., which we refer to as “Stephens,” rendered its oral opinion to the First Bancshares board of directors, subsequently confirmed in writing, that, as of such date and based upon and subject to the factors and assumptions set forth in its opinion, the merger consideration to be paid to the holders of First Bancshares common stock in the First Bancshares merger was fair, from a financial point of view, to such holders.

The full text of the Stephens opinion, which sets forth the assumptions made, matters considered and limits on the review undertaken, is attached as Appendix G to this proxy statement/prospectus and is incorporated herein by reference. The summary of the Stephens opinion set forth in this proxy statement/prospectus is qualified in its entirety by reference to the full text of such opinion. First Bancshares’ shareholders are urged to read the opinion in its entirety. Stephens’ written opinion was addressed to the First Bancshares board of directors (in its capacity as such) in connection with and for the purposes of its evaluation of the First Bancshares merger, was directed only to the merger consideration to be paid to the holders of First Bancshares common stock in the First Bancshares merger and did not address any other aspect of the First Bancshares merger. Stephens expressed no opinion as to the fairness of any consideration to be paid in connection with the First Bancshares merger to the holders of any other class of securities, creditors or other constituencies of First Bancshares or as to the underlying decision by First Bancshares to engage in the First Bancshares merger. The issuance of Stephens’ opinion was approved by a fairness committee of Stephens. The opinion does not constitute a recommendation to any shareholder of First Bancshares as to how such shareholder should vote with respect to the First Bancshares merger or any other matter.

For more information, see the section entitled “The First Bancshares Merger—Opinion of First Bancshares’ Financial Advisor” beginning on page 54 and the copy of the Stephens opinion included in this proxy statement/prospectus as Appendix G.

Financial Interests of First Bancshares’ Directors and Executive Officers in the First Bancshares Merger (page 64)

First Bancshares’ executive officers and directors may have interests in the First Bancshares merger that are different from, or in addition to, the interests of First Bancshares’ shareholders generally. Such interests include payments in connection with existing change in control and deferred cash incentive agreements with certain executive officers of First Bancshares and FirstCapital Bank, FirstCapital Bank and Prosperity Bank entering into new employment agreements with certain executive officers of First Bancshares and FirstCapital Bank, the

acceleration and settlement of certain outstanding equity awards, and the right to indemnification and insurance coverage following the consummation of the First Bancshares merger. The members of the First Bancshares board of directors were aware of and considered these interests, among other matters, when they approved the First Bancshares reorganization agreement and recommended that First Bancshares shareholders approve the First Bancshares merger proposal. These interests are described in more detail under the section entitled “The First Bancshares Merger—Financial Interests of First Bancshares’ Directors and Executive Officers in the First Bancshares Merger.”

Prosperity’s Reasons for the First Bancshares Merger (page 54)

The Prosperity board of directors adopted and approved the First Bancshares reorganization agreement. See the section entitled “The First Bancshares Merger—Prosperity’s Reasons for the First Bancshares Merger” on page 54 for a more detailed discussion of the factors considered by the Prosperity board of directors in reaching its decision to approve the First Bancshares reorganization agreement, including the First Bancshares merger and all transactions contemplated thereby.

The First Bancshares Special Meeting (page 39)

The First Bancshares special meeting will be held virtually on [ ], 2023, at [ ], Central Time. In order to attend the First Bancshares special meeting, please register before the special meeting date from your computer, tablet or smartphone by accessing the following link: [https://fcbtexas.com/FBOTMeeting]. After registering, you will receive a confirmation email containing information about joining the First Bancshares special meeting virtually. There will not be a physical meeting to attend in person.

At the First Bancshares special meeting, First Bancshares shareholders will be asked to consider and vote on the First Bancshares merger proposal and, if necessary or appropriate, the First Bancshares adjournment proposal.

First Bancshares has set the close of business on [ ], 2023 as the First Bancshares record date to determine which First Bancshares shareholders will be entitled to receive notice of, to attend and to vote at the First Bancshares special meeting. Each holder of shares of First Bancshares common stock outstanding on the First Bancshares record date will be entitled to one vote for each share held of record. As of the First Bancshares record date, there were [ ] shares of First Bancshares common stock outstanding and entitled to vote at the First Bancshares special meeting. As of the First Bancshares record date, the directors and executive officers of First Bancshares and their affiliates beneficially owned and were entitled to vote approximately [ ] shares of First Bancshares common stock, representing approximately [ ]% of the shares of First Bancshares common stock outstanding on that date.

Approval of the First Bancshares merger proposal requires the affirmative vote of holders of at least two-thirds of the outstanding shares of First Bancshares common stock entitled to vote on the First Bancshares merger proposal. Approval of the First Bancshares adjournment proposal requires the affirmative vote of holders of at least a majority of the outstanding shares of First Bancshares common stock entitled to vote on the proposal who are present in person or represented by proxy at the First Bancshares special meeting. A quorum is not required for a vote on the First Bancshares adjournment proposal.

With respect to the First Bancshares merger proposal, if you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the First Bancshares special meeting, or if you fail to instruct your bank, broker or other nominee how to vote, it will have the same effect as a vote against the proposal. With respect to the First Bancshares adjournment proposal, if you are a First Bancshares shareholder who is present in person or represented by proxy at the First Bancshares special meeting and you mark “ABSTAIN” on your proxy, fail to

vote on the First Bancshares adjournment proposal or fail to instruct your bank, broker or other nominee how to vote with respect to the First Bancshares adjournment proposal, it will have the same effect as a vote against the proposal. If you are not present in person or represented by proxy at the First Bancshares special meeting, it will have no effect on the First Bancshares adjournment proposal.

The Lone Star Merger (page 67)

Proposed Merger of Lone Star into Prosperity (page 67)

Under the terms and subject to the conditions of the Lone Star reorganization agreement, among other things, Lone Star will merge with and into Prosperity, with Prosperity as the surviving corporation in the Lone Star merger. Immediately following the Lone Star merger, Lone Star Bank will merge with and into Prosperity Bank, with Prosperity Bank as the surviving bank.

Terms of the Lone Star Merger (page 67)

The terms and conditions of the Lone Star merger are contained in the Lone Star reorganization agreement, which is attached to this proxy statement/prospectus as Appendix B. We urge you to read the Lone Star reorganization agreement carefully and in its entirety, as it is the legal document governing the Lone Star merger. All descriptions in this summary and elsewhere in this proxy statement/prospectus of the terms and conditions of the Lone Star merger are subject to, and qualified in their entirety by reference to, the Lone Star reorganization agreement.

Lone Star Merger Consideration (page 90)

If the Lone Star reorganization agreement is approved by the Lone Star shareholders and the Lone Star merger is subsequently completed, all shares of Lone Star common stock issued and outstanding immediately prior to the Lone Star effective time will be converted into an aggregate of 2,376,182 shares of Prosperity common stock and $64,053,717 in cash, less any amounts paid at closing with respect to outstanding equity awards, as set forth in the Lone Star reorganization agreement. Additionally, the aggregate Lone Star cash consideration will be reduced on a dollar-for-dollar basis if Lone Star’s equity capital, as calculated under the Lone Star reorganization agreement, is less than $121,088,508 at closing of the Lone Star merger. Because of the possibility of an adjustment to the Lone Star cash consideration, you will not know the exact amount of cash you will receive in connection with the Lone Star merger when you vote on the Lone Star reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each Lone Star shareholder will receive.

receive, in lieu thereof, an amount in cash, rounded up to the nearest whole cent (without interest), determined by multiplying (i) the fraction of a share (rounded to the nearest thousandth when expressed in decimal form) of Prosperity common stock that such Lone Star shareholder would otherwise be entitled to receive by (ii) the Lone Star/Prosperity average price.

Prosperity and Lone Star also have agreed that if any required regulatory approval requires divestitures in certain markets, Lone Star would accrue one-half of the cost associated with any such divestitures for purposes of its closing equity capital, up to $16 million.

Treatment of Equity Awards—Lone Star Stock Options and Stock Appreciation Rights (page 92)

At the Lone Star effective time, subject to the terms and conditions of the Lone Star reorganization agreement, each option granted by Lone Star to purchase shares of Lone Star common stock and each stock appreciation right under the Lone Star equity compensation plans will fully vest and be cancelled and converted into the right to receive a cash payment equal to the difference between the per award share merger consideration (as defined in the Lone Star reorganization agreement) and the per share exercise price (in the case of stock options) or initial value (in the case of stock appreciation rights) for each share of Lone Star common stock subject to such Lone Star stock option or stock appreciation right. Payments to holders of Lone Star stock options or stock appreciation rights will reduce the aggregate cash consideration to be paid to Lone Star shareholders.

Lone Star’s Reasons for the Lone Star Merger and Recommendation of the Lone Star Board of Directors (page 70)

Based on the reasons discussed elsewhere in this proxy statement/prospectus, the Lone Star board of directors believes that the Lone Star merger is in the best interests of Lone Star and the shareholders of Lone Star and recommends that Lone Star shareholders vote “FOR” the Lone Star merger proposal and “FOR” the Lone Star adjournment proposal. For a discussion of the circumstances surrounding the Lone Star merger and the factors considered by the Lone Star board of directors in approving the Lone Star reorganization agreement, see the discussion beginning on page 70.

Opinion of Lone Star’s Financial Advisor (page 73; Appendix H)

At the meeting of the Lone Star board of directors on October 7, 2022, Lone Star’s financial advisor, Stephens, rendered its oral opinion to the Lone Star board of directors, subsequently confirmed in writing, that, as of such date and based upon and subject to the factors and assumptions set forth in its opinion, the merger consideration to be paid to the holders of Lone Star common stock in the Lone Star merger was fair, from a financial point of view, to such holders.

The full text of the Stephens opinion, which sets forth the assumptions made, matters considered and limits on the review undertaken, is attached as Appendix H to this proxy statement/prospectus and is incorporated herein by reference. The summary of the Stephens opinion set forth in this proxy statement/prospectus is qualified in its entirety by reference to the full text of such opinion. Lone Star’s shareholders are urged to read the opinion in its entirety. Stephens’ written opinion was addressed to the Lone Star board of directors (in its capacity as such) in connection with and for the purposes of its evaluation of the Lone Star merger, was directed only to the merger consideration to be paid to the holders of Lone Star common stock in the Lone Star merger and did not address any other aspect of the Lone Star merger. Stephens expressed no opinion as to the fairness of any consideration to be paid in connection with the Lone Star merger to the holders of any other class of securities, creditors or other constituencies of Lone Star or as to the underlying decision by Lone Star to engage in the Lone Star merger. The issuance of Stephens’ opinion was approved by a fairness committee of Stephens. The opinion does not constitute a recommendation to any shareholder of Lone Star as to how such shareholder should vote with respect to the Lone Star merger or any other matter.

For more information, see the section entitled “The Lone Star Merger—Opinion of Lone Star’s Financial Advisor” beginning on page 73 and the copy of the Stephens opinion included in this proxy statement/prospectus as Appendix H.

Financial Interests of Lone Star’s Directors and Executive Officers in the Lone Star Merger (page 83)

Lone Star’s executive officers and directors may have interests in the Lone Star merger that are different from, or in addition to, the interests of Lone Star’s shareholders generally. Such interests include payments in connection with existing employment agreements and change in control severance plans with certain executive officers, Prosperity Bank and Lone Star Bank entering into new employment agreements with certain of Lone Star Bank’s executive officers, the acceleration and settlement of certain outstanding equity awards, and the right to indemnification and insurance coverage following the consummation of the Lone Star merger. The members of the Lone Star board of directors were aware of and considered these interests, among other matters, when they approved the Lone Star reorganization agreement and recommended that Lone Star shareholders approve the Lone Star merger proposal. These interests are described in more detail under the section entitled “The Lone Star Merger—Financial Interests of Lone Star’s Directors and Executive Officers in the Lone Star Merger” beginning on page 83.

Prosperity’s Reasons for the Lone Star Merger (page 73)

The Prosperity board of directors adopted and approved the Lone Star reorganization agreement. See the section entitled “The Lone Star Merger—Prosperity’s Reasons for the Lone Star Merger” on page 73 for a more detailed discussion of the factors considered by the Prosperity board of directors in reaching its decision to approve the Lone Star reorganization agreement, including the Lone Star merger and all transactions contemplated thereby.

The Lone Star Special Meeting (page 43)

The Lone Star special meeting will be held on [ ], 2023, at [ ], Central Time, at 6220 Milwaukee Avenue, Lubbock, Texas 79424. At the Lone Star special meeting, Lone Star shareholders will be asked to consider and vote on the Lone Star merger proposal and, if necessary or appropriate, the Lone Star adjournment proposal.

Lone Star has set the close of business on [ ], 2023 as the Lone Star record date to determine which Lone Star shareholders will be entitled to receive notice of, attend and vote at the Lone Star special meeting. Each holder of shares of Lone Star common stock outstanding on the Lone Star record date will be entitled to one vote for each share held of record. As of the Lone Star record date, there were [ ] shares of Lone Star common stock outstanding and entitled to vote at the Lone Star special meeting. As of the Lone Star record date, the directors and executive officers of Lone Star and their affiliates beneficially owned and were entitled to vote approximately [ ] shares of Lone Star common stock, representing approximately [ ]% of the shares of Lone Star common stock outstanding on that date.

Approval of the Lone Star merger proposal requires the affirmative vote of holders of at least two-thirds of the outstanding shares of Lone Star common stock entitled to vote on the Lone Star merger proposal. Approval of the adjournment proposal requires the affirmative vote of holders of at least a majority of the outstanding shares of Lone Star common stock entitled to vote on the proposal who are present in person or represented by proxy at the Lone Star special meeting. A quorum is not required for a vote on the Lone Star adjournment proposal.

With respect to the Lone Star merger proposal, if you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the Lone Star special meeting, or if you fail to instruct your bank, broker or other

nominee how to vote, it will have the same effect as a vote against the proposal. With respect to the Lone Star adjournment proposal, if you are a Lone Star shareholder who is present in person or represented by proxy at the Lone Star special meeting and you mark “ABSTAIN” on your proxy, fail to vote on the Lone Star adjournment proposal or fail to instruct your bank, broker, or other nominee how to vote with respect to the proposal, it will have the same effect as a vote against the proposal. If you are not present in person or represented by proxy at the Lone Star special meeting, it will have no effect on the Lone Star adjournment proposal.

The Mergers (page 85)

Board of Directors and Management of Prosperity and Prosperity Bank After the Mergers (page 85)

Prosperity Plans to Continue Payment of Quarterly Dividends (page 119)

As approved by Prosperity’s board of directors, Prosperity declared and paid a $0.46 per share dividend to holders of Prosperity common stock for the first three fiscal quarters of 2020 and a $0.49 per share dividend for the fourth fiscal quarter of 2020 and the first three fiscal quarters of 2021. Prosperity declared and paid a $0.52 per share dividend for the last fiscal quarter of 2021 and the first three fiscal quarters of 2022. Prosperity declared and paid a $0.55 per share dividend for the fourth fiscal quarter of 2022.

Prosperity intends to continue to pay regular quarterly cash dividends on its common stock in the first fiscal quarter of 2023 and following the mergers, when, as and if declared by Prosperity’s board of directors out of funds legally available for that purpose and subject to regulatory restrictions.

Issued Prosperity Shares Will Be Eligible for Trading (page 85)

Prosperity common stock is listed on the NYSE under the symbol “PB.” The Prosperity common stock issuable in the mergers will be listed on the NYSE.

Under the reorganization agreements, Prosperity has agreed to file all documents required to be filed to have the shares of Prosperity common stock to be issued approved for listing on the NYSE prior to closing of each of the mergers and to use its commercially reasonable efforts to effect such listing. The obligations of the parties to complete the respective mergers are subject to such shares having been approved for listing on the NYSE and such approval having not been withdrawn or revoked.

Market Prices of Prosperity Common Stock (page 119)

Shares of Prosperity common stock are quoted on the NYSE under the symbol “PB.” On October 7, 2022, the last trading day before the mergers were announced, the closing price of Prosperity common stock on the NYSE was $69.27 per share. On [ ], 2023, the most recent practicable date prior to the date of this proxy statement/prospectus, the closing price of Prosperity common stock on the NYSE was $[ ] per share. The market price of Prosperity common stock will fluctuate prior to the mergers, including between the respective shareholder meetings and closings. Shares of First Bancshares and Lone Star are not traded on any established public trading market.

Accounting Treatment (page 109)

The mergers will be accounted for as acquisitions of First Bancshares and Lone Star by Prosperity and of FirstCapital Bank and Lone Star Bank by Prosperity Bank under the acquisition method of accounting in

accordance with the Financial Accounting Standards Board’s Accounting Standard Codification Topic 805, Business Combinations.

Dissenters’ Rights of Appraisal in the Mergers (page 85)

As a shareholder of First Bancshares or Lone Star, under Texas law you have the right to dissent from the applicable merger and have the appraised fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable, paid to you in cash. The appraised fair value may be more or less than the value of the shares of Prosperity common stock and cash being paid in the applicable merger.

Persons having beneficial interests in First Bancshares common stock or Lone Star common stock held of record in the name of another person, such as a broker or bank, must act promptly to cause the record holder to take the actions required under Texas law to exercise your dissenter’s rights.

In order to dissent, you must carefully follow the requirements of the TBOC, including giving the required written notice prior to the special meeting at which the vote on the applicable reorganization agreement is taken, voting against the reorganization agreement and filing a written demand with Prosperity within 20 days after completion of the applicable merger for payment of the fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable. These steps are summarized under the caption “The Mergers—Dissenters’ Rights of Appraisal” beginning on page 85.

If you intend to exercise dissenters’ rights, you should read the statutes carefully and consult with your own legal counsel. You should also remember that if you return a signed proxy card but fail to provide instructions as to how your shares of First Bancshares common stock or Lone Star common stock, as applicable, are to be voted, you will be considered to have voted in favor of the applicable reorganization agreement and you will not be able to assert dissenters’ rights. Also, if you exercise dissenters’ rights, you may have taxable income as a result, so we recommend that you consult with your own tax advisor if you intend to dissent.

If the First Bancshares reorganization agreement is approved by the shareholders of First Bancshares, holders of First Bancshares common stock who make a written objection to the First Bancshares merger prior to the First Bancshares special meeting, vote against the approval of the First Bancshares reorganization agreement, properly make a written demand for payment following notice of the First Bancshares merger and timely surrender their First Bancshares stock certificates will be entitled to receive the appraised fair value of their shares in cash under the TBOC.

If the Lone Star reorganization agreement is approved by the shareholders of Lone Star, holders of Lone Star common stock who make a written objection to the Lone Star merger prior to the Lone Star special meeting, vote against the approval of the Lone Star reorganization agreement, properly make a written demand for payment following notice of the Lone Star merger and timely surrender their Lone Star stock certificates will be entitled to receive the appraised fair value of their shares in cash under the TBOC.

The text of the provisions of the TBOC pertaining to dissenters’ rights is attached to this proxy statement/prospectus as Appendix I.

Regulatory Approvals Required for the Mergers (page 87)

The acquisitions of First Bancshares and Lone Star by Prosperity each require the approval of the Board of Governors of the Federal Reserve System, which we refer to as the “Federal Reserve,” unless the requirement for such approval is waived by the Federal Reserve. On November 18, 2022, Prosperity filed the required documentation with the Federal Reserve Bank of Dallas to request a waiver of approval with respect to the Lone

Star merger. On November 21, 2022, Prosperity filed the required documentation with the Federal Reserve Bank of Dallas to request a waiver of approval with respect to the First Bancshares merger.

The mergers of FirstCapital Bank and Lone Star Bank with and into Prosperity Bank each require the approval of the Federal Deposit Insurance Corporation, which we refer to as the “FDIC,” and the Texas Department of Banking, which we refer to as the “TDB.” On November 16, 2022, Prosperity Bank and Lone Star Bank filed the required applications with the FDIC and TDB; and on November 17, 2022, Prosperity Bank and FirstCapital Bank filed the required applications with the FDIC and TDB.

In addition to the FDIC, the Antitrust Division of the Department of Justice conducts a concurrent competitive review of the mergers to analyze each merger’s competitive effects and determine whether either merger would result in a violation of antitrust laws.

Effective Time of the Mergers (page 92)

Each merger will become effective at the date and time specified in the certificate of merger filed with respect to such merger with the Texas Secretary of State. Subject to the receipt of applicable shareholder and regulatory approvals, and the satisfaction or waiver of the other conditions to the parties’ obligations to effect the respective mergers, we anticipate that the mergers will be completed in the first quarter of 2023, although delays could occur.

We cannot assure you that the necessary shareholder and governmental approvals will be obtained or that the other conditions to completion of the mergers can or will be satisfied or waived.

Exchange Procedures (page 92)

As soon as practicable after the effective time of the applicable merger, you will receive a letter and instructions from Computershare Investor Services, Prosperity’s exchange agent, with respect to the procedures for surrendering your stock certificates in exchange for cash and shares of Prosperity common stock. You must carefully review and complete these materials and return them as instructed along with your stock certificates for First Bancshares common stock or Lone Star common stock, as applicable. Please do not send First Bancshares, Lone Star or Prosperity any stock certificates until you receive these instructions.

The Reorganization Agreements (page 89)

Conditions to Completion of the Mergers (page 93)

The completion of the respective mergers depends on a number of conditions being met. These include, among others:

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receipt of all required regulatory approvals;

•

approval of the applicable reorganization agreement by the First Bancshares shareholders or Lone Star shareholders, as applicable;

•

receipt by each party of an opinion of such party’s counsel to the effect that the applicable merger will qualify as a reorganization under Section 368(a) of the Code;

•

the shares of Prosperity common stock to be issued to First Bancshares shareholders and Lone Star shareholders being registered with the SEC and authorized for listing on the NYSE;

•

the other party’s representations and warranties contained in the applicable reorganization agreement being true and correct in all material respects as of the date of such reorganization agreement and the closing date of the applicable merger;

•

the absence of a material adverse change in the assets, properties, business or financial condition of either party to the applicable reorganization agreement or any event that could reasonably be expected to cause or result in a material adverse effect on either party to the applicable reorganization agreement;

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each director, each executive officer and certain other officers of First Bancshares and FirstCapital Bank and Lone Star and Lone Star Bank, as applicable, having executed a release agreement;

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with respect to the First Bancshares merger, termination of certain deferred cash incentive agreements by FirstCapital Bank and execution of a termination and release agreement by each such employee;

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with respect to the Lone Star merger, cancellation of all outstanding stock options by Lone Star and execution of a cancellation and release agreement by each holder of a Lone Star stock option;

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certain officers of First Bancshares and/or FirstCapital Bank and Lone Star and/or Lone Star Bank, as applicable, each will have entered into an employment agreement with Prosperity;

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each non-employee director of First Bancshares and FirstCapital Bank and Lone Star and Lone Star Bank, as applicable, having entered into a support (non-competition) agreement with Prosperity, which agreements have been executed;

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with respect to the First Bancshares merger, the allowance for loan losses of First Bancshares as of the closing date being equal to at least 1.36% of its total loans, subject to certain adjustments; and

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with respect to the Lone Star merger, the allowance for loan losses of Lone Star as of the closing date being equal to at least 1.25% of its total loans, subject to certain adjustments.

Any condition to the completion of the applicable merger, except the required shareholder and regulatory approvals, and the absence of an order or ruling prohibiting the merger, may be waived in writing by the party to the applicable reorganization agreement entitled to the benefit of such condition.

Amendment or Waiver of the Reorganization Agreements (page 106)

Prosperity and First Bancshares or Lone Star, as applicable, may amend the applicable reorganization agreement and each party to such reorganization agreement may waive its right to require the other party to adhere to any term or condition of the reorganization agreement. However, the merger consideration to be received by the First Bancshares shareholders and the Lone Star shareholders pursuant to the terms of the applicable reorganization agreement may not be decreased after the approval of the reorganization agreement by the First Bancshares shareholders and the Lone Star shareholders, as applicable, without further approval by the First Bancshares shareholders and the Lone Star shareholders, as applicable.

Termination of the Reorganization Agreements (page 104)

The parties to each reorganization agreement may mutually agree at any time to terminate such agreement without completing the applicable merger. In addition, either party to a reorganization agreement may decide, without the consent of the other, to terminate such reorganization agreement if:

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any order, decree or ruling or any other action that seeks to restrain, enjoin or prohibit the First Bancshares merger or the Lone Star merger, as applicable, is issued, and such order, decree, ruling or other action is final and non-appealable;

•

in the case of the First Bancshares merger, the merger has not been completed by May 8, 2023 (unless one or more of the regulatory approvals has not been received on or before May 8, 2023, in which case this deadline will be extended to July 7, 2023), or in the case of the Lone Star merger, the merger has not been completed by April 8, 2023 (unless one or more of the regulatory approvals has not been received on or before April 8, 2023, in which case this deadline will be extended to June 7, 2023), or such later date approved in writing by the boards of directors of Prosperity and First Bancshares or Lone Star, as applicable, unless the failure to complete the applicable merger by that time is due to a violation of the applicable reorganization agreement by the party that seeks to terminate such reorganization agreement;

•

the merger of First Bancshares into Prosperity or the merger of FirstCapital Bank into Prosperity Bank, in the case of the First Bancshares reorganization agreement, or the merger of Lone Star into Prosperity or the merger of Lone Star Bank into Prosperity Bank, in the case of the Lone Star reorganization agreement, is not approved by the appropriate regulatory authorities or the application or notices are suggested or recommended to be withdrawn by any regulatory authorities;

•

the other party to the applicable reorganization agreement materially breaches its representations and warranties or any covenant or agreement contained in such reorganization agreement and such breach has not been cured within 15 days after the terminating party gives written notice of such failure to the breaching party; or First Bancshares shareholders or Lone Star shareholders, as applicable, fail to approve the applicable reorganization agreement.

First Bancshares or Lone Star may terminate its reorganization agreement, without the consent of Prosperity, if the board of directors of First Bancshares or Lone Star, as applicable, receives an unsolicited, bona fide alternative “acquisition proposal” (as defined in each reorganization agreement) and, under certain terms and conditions, determines that it is a superior proposal to that of the applicable reorganization agreement and that the failure to accept such proposal would cause the First Bancshares board of directors or Lone Star board of directors, as applicable, to violate its fiduciary duties under applicable law; but First Bancshares or Lone Star, as applicable, must notify Prosperity of the superior proposal at least five business days before terminating the applicable reorganization agreement, during which time Prosperity has the right to adjust the terms and conditions of the applicable reorganization agreement so that the superior proposal no longer constitutes a superior proposal.

Prosperity may terminate the First Bancshares reorganization agreement, without the consent of First Bancshares, if any required regulatory approval is obtained subject to restrictions or conditions on the operations of First Bancshares, FirstCapital Bank, Prosperity or Prosperity Bank that are reasonably unacceptable to Prosperity.

Prosperity may terminate the Lone Star reorganization agreement, without the consent of Lone Star, if any required regulatory approval is obtained subject to restrictions or conditions on the operations of Lone Star, Lone Star Bank, Prosperity or Prosperity Bank that are reasonably unacceptable to Prosperity.

Prosperity may also terminate the applicable reorganization agreement if First Bancshares or Lone Star, as applicable, has materially breached its non-solicitation obligations contained in the applicable reorganization agreement in a manner adverse to Prosperity; the First Bancshares board of directors or the Lone Star board of directors, as applicable, resolves to accept a competing acquisition proposal; or the First Bancshares board of directors or the Lone Star board of directors, as applicable, changes its recommendation regarding the applicable merger.

Termination Fees and Effect of Termination (page 104)

If the First Bancshares reorganization agreement or the Lone Star reorganization agreement, as applicable, is terminated by:

•

Prosperity because First Bancshares or Lone Star, as applicable, materially breaches the non-solicitation obligations set forth in the applicable reorganization agreement in a manner adverse to Prosperity;

•

Prosperity because the First Bancshares board of directors or Lone Star board of directors, as applicable, resolves to accept another acquisition proposal;

•

Prosperity because the First Bancshares board of directors or Lone Star board of directors, as applicable, withdraws, amends or modifies, in any manner adverse to Prosperity, its recommendation or approval of the applicable reorganization agreement or the applicable merger; or

•

First Bancshares or Lone Star, as applicable, because the First Bancshares board of directors or Lone Star board of directors, as applicable, receives an unsolicited, bona fide alternative acquisition proposal and, under certain terms and conditions, determines that it is a superior proposal to that of the applicable reorganization agreement taking into account any adjustments made by Prosperity to the applicable merger consideration,

then, unless Prosperity is in material breach of any covenant or obligation under the applicable reorganization agreement, First Bancshares and Lone Star, as applicable, will be required to pay Prosperity a termination fee of $13,665,708 and $9,146,074, respectively.

If either Prosperity or First Bancshares terminates the First Bancshares reorganization agreement and:

•

such termination occurs after May 8, 2023 (or July 7, 2023, if regulatory approval has not been obtained by May 8, 2023), if at the time of termination, the registration statement of which this proxy statement/prospectus is a part has been declared effective for at least 25 business days prior to such termination and First Bancshares has failed to call, give notice of, convene and hold the First Bancshares special meeting by such date and an acquisition proposal exists at the time of termination, or

•

without regard to timing, First Bancshares’ shareholders have not approved the First Bancshares reorganization agreement and an acquisition proposal exists at the time of termination,

then, unless Prosperity is in material breach of any covenant or obligation under the reorganization agreement, First Bancshares will be required to pay Prosperity up to $2,000,000 for its expenses related to the First Bancshares merger.

If either Prosperity or Lone Star terminates the Lone Star reorganization agreement and:

•

such termination occurs after April 8, 2023 (or June 7, 2023, if regulatory approval has not been obtained by April 8, 2023), if at the time of termination, the registration statement of which this proxy statement/prospectus is a part has been declared effective for at least 25 business days prior to such termination and Lone Star has failed to call, give notice of, convene and hold the Lone Star special meeting by such date and an acquisition proposal exists at the time of termination, or

•

without regard to timing, Lone Star’s shareholders have not approved the Lone Star reorganization agreement and an acquisition proposal exists at the time of termination,

then, unless Prosperity is in material breach of any covenant or obligation under the reorganization agreement, Lone Star will be required to pay Prosperity up to $2,000,000 for its expenses related to the Lone Star merger.

If either Prosperity or First Bancshares terminates the First Bancshares reorganization agreement, within twelve months of termination of the First Bancshares reorganization agreement First Bancshares enters into an acquisition agreement with a third party and:

•

such termination occurs after May 8, 2023 (or July 7, 2023, if regulatory approval has not been obtained by May 8, 2023), if at the time of termination, First Bancshares’ shareholders have not approved the First Bancshares reorganization agreement and an acquisition proposal exists at the time of termination, or

•

without regard to timing, First Bancshares’ shareholders have not approved the First Bancshares reorganization agreement and an acquisition proposal exists at the time of termination,

then, unless Prosperity is in material breach of any covenant or obligation under the reorganization agreement, First Bancshares will be required to pay Prosperity a termination fee of $13,665,708 minus any of Prosperity’s expenses related to the First Bancshares merger paid by First Bancshares.

If either Prosperity or Lone Star terminates the Lone Star reorganization agreement, within twelve months of termination of the Lone Star reorganization agreement Lone Star enters into an acquisition agreement with a third party and:

•

such termination occurs after April 8, 2023 (or June 8, 2023, if regulatory approval has not been obtained by April 8, 2023), if at the time of termination, Lone Star’s shareholders have not approved the Lone Star reorganization agreement and an acquisition proposal exists at the time of termination, or

•

without regard to timing, Lone Star’s shareholders have not approved the Lone Star reorganization agreement and an acquisition proposal exists at the time of termination,

then, unless Prosperity is in material breach of any covenant or obligation under the reorganization agreement, Lone Star will be required to pay Prosperity a termination fee of $9,146,074 minus any of Prosperity’s expenses related to the Lone Star merger paid by Lone Star.

Material U.S. Federal Income Tax Consequences of the Mergers (page 110)

Each of the First Bancshares merger and the Lone Star merger is intended to qualify as a “reorganization” within the meaning of Section 368(a) of the Code, and it is a condition to the respective obligations of Prosperity and First Bancshares, with respect to the First Bancshares merger, and of Prosperity and Lone Star, with respect to the Lone Star merger, to complete the applicable merger that each party receives a legal opinion from its counsel to that effect.

Consistent with such treatment, a U.S. holder (as defined in the section entitled “Material U.S. Federal Income Tax Consequences of the Mergers” beginning on page 110) of First Bancshares common stock or Lone Star common stock will not recognize gain or loss for U.S. federal income tax purposes upon the exchange of their shares of First Bancshares common stock or Lone Star common stock, as applicable, for shares of Prosperity common stock, except that a U.S. holder generally will recognize gain (but not loss) in an amount equal the lesser of (a) the cash consideration received (excluding cash received in lieu of a fractional share) and (b) the gain realized. The amount of gain realized by a U.S. holder will be equal to the amount by which the cash (excluding cashed received in lieu of fractional shares) plus the fair market value, at the effective time of the applicable merger, of the Prosperity common stock received exceeds the holder’s adjusted tax basis in the First Bancshares common stock or Lone Star common stock, as applicable, to be surrendered in exchange therefor.

The tax consequences to a U.S. holder of First Bancshares common stock or Lone Star common stock, as applicable, described above may not apply to all holders of First Bancshares or Lone Star common stock or the First Bancshares or Lone Star shareholders who exercise their dissenters’ rights. In addition, you may be subject

to state, local or non-U.S. tax laws that are not discussed in this proxy statement/prospectus. Accordingly, we strongly urge holders of First Bancshares common stock and Lone Star common stock to consult their own tax advisors for a full understanding of the particular tax consequences of the applicable merger to them.

Comparison of Rights of Shareholders of Prosperity and First Bancshares, and Prosperity and Lone Star (pages 125 and 130)

Each of First Bancshares and Lone Star is a Texas corporation and the rights of their respective shareholders are governed by Texas law and their respective certificates of formation and bylaws. Prosperity is a Texas corporation and the rights of Prosperity shareholders are governed by Texas law and Prosperity’s articles of incorporation and bylaws. Upon completion of each merger, the shareholders of First Bancshares and Lone Star will become shareholders of Prosperity and their rights will be governed by Prosperity’s articles of incorporation and bylaws in addition to Texas law. Prosperity’s articles of incorporation and bylaws will remain the same following the mergers unless later altered, amended or repealed.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

Certain statements contained in this proxy statement/prospectus that are not statements of historical fact constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks and uncertainties and are made pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1933, as amended, which we refer to as the “Securities Act,” and Section 21E of the Securities Exchange Act of 1934, as amended, which we refer to as the “Exchange Act.” These forward-looking statements include information about possible or assumed future results of operations of Prosperity, First Bancshares or Lone Star before or after the respective mergers are completed as well as information about the respective mergers, including Prosperity’s, First Bancshares’ or Lone Star’s future revenues, income, expenses, provision for taxes, effective tax rate, earnings per share and cash flows, Prosperity’s, First Bancshares’ or Lone Star’s future capital expenditures and dividends, Prosperity’s, First Bancshares’ or Lone Star’s future financial condition and changes therein, including changes in Prosperity’s, First Bancshares’ or Lone Star’s loan portfolio and allowance for loan losses, Prosperity’s, First Bancshares’ or Lone Star’s future capital structure or changes therein, the plan and objectives of management for future operations, Prosperity’s future or proposed acquisitions, the future or expected effect of acquisitions on Prosperity’s operations, results of operations and financial condition, Prosperity’s, First Bancshares’ or Lone Star’s future economic performance, statements about the benefits of the proposed transaction, and the statements of the assumptions underlying any such statement. Such statements are typically, but not exclusively, identified by the use in the statements of words or phrases such as “aim,” “anticipate,” “estimate,” “expect,” “goal,” “guidance,” “intend,” “is anticipated,” “is estimated,” “is expected,” “is intended,” “objective,” “plan,” “projected,” “projection,” “will affect,” “will be,” “will continue,” “will decrease,” “will grow,” “will impact,” “will increase,” “will incur,” “will reduce,” “will remain,” “will result,” “would be,” variations of such words or phrases (including where the word “could,” “may” or “would” is used rather than the word “will” in a phrase) and similar words and phrases indicating that the statement addresses some future result, occurrence, plan or objective. The forward-looking statements that Prosperity, First Bancshares and Lone Star make are based on Prosperity’s, First Bancshares’ and Lone Star’s current expectations and assumptions regarding Prosperity’s, First Bancshares’ and Lone Star’s businesses, the economy and other future conditions. Because forward-looking statements relate to future results and occurrences, they are subject to inherent uncertainties, risks, and changes in circumstances that are difficult to predict. Many possible events or factors could affect the future financial results and performance of each of Prosperity, First Bancshares and Lone Star before the mergers or Prosperity after the mergers, and could cause those results or performance to differ materially from those expressed in the forward-looking statements. These possible events or factors include, but are not limited to:

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Prosperity’s, First Bancshares’ or Lone Star’s ability to sustain its current internal growth rate and total growth rate;

•

changes in geopolitical, business and economic events, occurrences and conditions, including changes in rates of inflation or deflation, nationally, regionally and in Prosperity’s, First Bancshares’ or Lone Star’s target markets, particularly in Texas;

•

worsening business and economic conditions nationally, regionally and in Prosperity’s, First Bancshares’ or Lone Star’s target markets, particularly in Texas, and the geographic areas in Texas in which Prosperity, First Bancshares or Lone Star operate;

•

the occurrence of any event, change or other circumstances that could give rise to the right of one or both of the parties to each reorganization agreement to terminate such reorganization agreement;

•

the outcome of any legal proceedings that may be instituted against Prosperity, First Bancshares or Lone Star;

•

delays in completing either or both of the mergers;

•

the failure to obtain necessary regulatory approvals (and the risk that such approvals may result in the imposition of conditions that could adversely affect the combined company or the expected benefits of

the transactions) and shareholder approvals or to satisfy any of the other conditions to the mergers on a timely basis or at all;

•

the possibility that the anticipated benefits of either or both of the mergers are not realized when expected or at all, including as a result of the impact of, or problems arising from, the integration of the companies or as a result of the strength of the economy and competitive factors in the areas where Prosperity, First Bancshares and Lone Star do business;

•

the possibility that the mergers may be more expensive to complete than anticipated, including as a result of unexpected factors or events, diversion of management’s attention from ongoing business operations and opportunities, potential adverse reactions or changes to business or employee relationships, including those resulting from the announcement or completion of the mergers, and Prosperity’s ability to complete the acquisition and integration of First Bancshares and Lone Star successfully;

•

the dilution caused by Prosperity’s issuance of additional shares of its common stock in connection with the transactions;

•

Prosperity’s revenues after the First Bancshares and Lone Star mergers may be less than expected;

•

Prosperity’s, First Bancshares’ or Lone Star’s dependence on their respective management teams and their ability to attract, motivate and retain qualified personnel;

•

the concentration of Prosperity’s, First Bancshares’ or Lone Star’s business within their respective geographic areas of operation in Texas;

•

changes in asset quality, including increases in default rates and loans and higher levels of nonperforming loans and loan charge-offs;

•

concentration of the loan portfolio of Prosperity Bank, FirstCapital Bank or Lone Star Bank in commercial and residential real estate loans and changes in the prices, values and sales volumes of commercial and residential real estate;

•

the ability of Prosperity Bank, FirstCapital Bank or Lone Star Bank to make loans with acceptable interest rates and levels of risk of repayment and to otherwise invest in assets at acceptable yields and presenting acceptable investment risks;

•

inaccuracy of the assumptions and estimates that the managements of Prosperity, First Bancshares or Lone Star make in establishing reserves for probable loan losses and other estimates;

•

lack of liquidity, including as a result of a reduction in the amount of sources of liquidity, that Prosperity, First Bancshares or Lone Star currently have;

•

material increases or decreases in the amount of deposits held by Prosperity Bank, FirstCapital Bank or Lone Star Bank and the cost of those deposits;

•

access to the debt and equity markets and the overall cost of funding operations;

•

regulatory requirements to maintain minimum capital levels or maintenance of capital at levels sufficient to support Prosperity’s anticipated growth;

•

changes in market interest rates that affect the pricing of the loans and deposits of each of Prosperity Bank, FirstCapital Bank and Lone Star Bank, and the net interest income of each of Prosperity Bank, FirstCapital Bank and Lone Star Bank;

•

fluctuations in the market value and liquidity of the securities Prosperity, First Bancshares or Lone Star hold for sale, including as a result of changes in market interest rates;

•

effects of competition from a wide variety of local, regional, national and other providers of financial, investment and insurance services;

•

changes in economic and market conditions that affect the amount and value of the assets of Prosperity Bank, FirstCapital Bank and Lone Star Bank;

•

the institution and outcome of, and costs associated with, litigation and other legal proceedings against one or more of Prosperity, Prosperity Bank, First Bancshares, FirstCapital Bank, Lone Star and Lone Star Bank, or to which any of such entities is subject;

•

the occurrence of market conditions adversely affecting the financial industry generally;

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the impact of recent and future legislative and regulatory changes, including changes in banking, securities and tax laws and regulations and their application by Prosperity’s regulators, such as the Dodd-Frank Act, and changes in federal government policies;

•

changes in accounting policies and practices, as may be adopted by the bank regulatory agencies, the Financial Accounting Standards Board, the SEC and the Public Company Accounting Oversight Board, as the case may be;

•

governmental monetary and fiscal policies, including the policies of the Federal Reserve;

•

changes in the scope and cost of FDIC insurance and other coverage;

•

the effects of war or other conflicts, acts of terrorism (including cyber attacks) or other catastrophic events, including storms, droughts, tornadoes, hurricanes and flooding, that may affect general economic conditions;

•

the impact of investments that Prosperity or Prosperity Bank may have made or may make and the changes in the value of those investments;

•

Prosperity’s ability to continue to identify acquisition targets and successfully acquire desirable financial institutions to sustain its growth, to expand its presence in its markets and to enter new markets;

•

general business and economic conditions in Prosperity’s, First Bancshares’ or Lone Star’s markets may change or may be less favorable than expected;

•

changes may occur in business conditions and inflation;

•

an increase in the rate of personal or commercial customers’ bankruptcies;

•

technology-related changes may be harder to make or may be more expensive than expected;

•

attacks on the security of, and breaches of, Prosperity’s, Lone Star’s, or First Bancshares’ digital information systems, the costs Prosperity, First Bancshares or Lone Star incurs to provide security against such attacks and any costs and liability Prosperity, Lone Star, or First Bancshares may incur in connection with any breach of those systems; and

•

the potential impact of technology and “FinTech” entities and digital currencies on the banking industry generally.

For other factors, risks and uncertainties that could cause actual results to differ materially from estimates contained in forward-looking statements, please read the “Risk Factors” section beginning on page 33 of this proxy statement/prospectus, and the “Risk Factors” sections of Prosperity’s Annual Report on Form 10-K for the year ended December 31, 2021 and subsequent Quarterly Reports on Form 10-Q, each of which is incorporated by reference into this proxy statement/prospectus. See “Where You Can Find More Information” beginning on page 141.

We urge you to consider all of these risks, uncertainties and other factors carefully in evaluating all such forward-looking statements made in this proxy statement/prospectus. As a result of these and other matters, including changes in facts, assumptions not being realized or other factors, the actual results relating to the

subject matter of any forward-looking statement may differ materially from the anticipated results expressed or implied in that forward-looking statement. Any forward-looking statement made in this proxy statement/prospectus or made by Prosperity in any report, filing, document or information incorporated by reference in this proxy statement/prospectus, speaks only as of the date on which it is made. Prosperity does not undertake any obligation to update any such forward-looking statement, whether as a result of new information, future developments or otherwise, except as may be required by law.

A forward-looking statement may include a statement of the assumptions or bases underlying the forward-looking statement. We believe that these assumptions or bases have been chosen in good faith and that they are reasonable. However, we caution you that assumptions as to future occurrences or results almost always vary from actual future occurrences or results, and the differences between assumptions and actual occurrences and results can be material. Therefore, we caution you not to place undue reliance on the forward-looking statements contained in this proxy statement/prospectus or incorporated by reference herein.

RISK FACTORS

In addition to general investment risks and the other information contained in or incorporated by reference into this proxy statement/prospectus, including the matters addressed in the section entitled “Cautionary Note Regarding Forward-Looking Statements,” and the matters discussed under the caption “Risk Factors” in Prosperity’s Annual Report on Form 10-K for the year ended December 31, 2021 and any updates to those risk factors set forth in Prosperity’s Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and other filings, which have been filed with the SEC, First Bancshares shareholders and Lone Star shareholders should carefully consider the following factors in deciding whether to vote for the proposals presented in this proxy statement/prospectus. See also the section entitled “Where You Can Find More Information” beginning on page 141.

Risks Relating to the Mergers

Because the market price of Prosperity common stock will fluctuate, shareholders of First Bancshares and Lone Star cannot be certain of the market value of the stock consideration they will receive upon completion of the applicable merger.

A significant portion of the merger consideration payable to the shareholders of First Bancshares and Lone Star under their respective reorganization agreements will be in the form of Prosperity common stock. The market value of Prosperity common stock will vary from the closing price of Prosperity common stock on the date that parties announced the mergers, on the date that this proxy statement/prospectus is mailed to the shareholders of First Bancshares and Lone Star, and on the dates of the special meetings, and any change in the market price of Prosperity common stock prior to the completion of the respective mergers will affect the value of the merger consideration that will be received by the shareholders of First Bancshares and Lone Star, as applicable. The market price of Prosperity common stock could be subject to significant fluctuations due to changes in sentiment in the market regarding Prosperity’s operations or business prospects, as well as from a variety of other factors. Therefore, at the time of the special meetings, shareholders of First Bancshares and Lone Star will not know the precise market value of any shares of Prosperity common stock that they may receive at the effective time of the respective mergers. Shareholders should obtain market quotations for shares of Prosperity common stock before voting their shares at the special meetings.

The equity capital of First Bancshares or Lone Star at closing of the applicable merger could be less than that required by the applicable reorganization agreement, which would result in the reduction of the amount of the cash consideration that First Bancshares shareholders or Lone Star shareholders would be entitled to receive.

The amount of cash consideration that First Bancshares shareholders would be entitled to receive in the First Bancshares merger will be reduced if First Bancshares’ equity capital is less than $204,000,000, in the manner and under the circumstances set forth in the First Bancshares reorganization agreement. The amount of cash consideration that Lone Star shareholders would be entitled to receive in the Lone Star merger will be reduced if Lone Star’s equity capital is less than $121,088,508, in the manner and under the circumstances set forth in the Lone Star reorganization agreement. Accordingly, at the time First Bancshares shareholders and Lone Star shareholders vote with respect to the respective reorganization agreements, they will not know the exact value of the cash consideration they will be entitled to receive in the First Bancshares merger or the Lone Star merger, respectively.

The respective mergers may not be completed, may take longer than expected or may be subject to conditions imposed by government entities that are not presently anticipated or cannot be met.

Completion of each of the mergers is subject to the receipt of applicable regulatory approvals or the waiver of application and prior approval requirements. On November 18, 2022 and November 21, 2022, Prosperity filed the required documentation with the Federal Reserve Bank of Dallas to request waivers of the Federal Reserve’s

application and prior approval requirements for the Lone Star merger and First Bancshares merger, respectively. On November 18, 2022, Prosperity Bank and Lone Star Bank filed the required applications with the FDIC and TDB, and on November 18, 2022, Prosperity Bank and FirstCapital Bank filed the required applications with the FDIC and TDB. In determining whether to grant these approvals, the regulators consider a variety of factors, including the regulatory standing of each party and the factors described under “The Mergers—Regulatory Approvals Required for the Mergers” beginning on page 87. An adverse development in the regulatory standing of either party to the applicable merger or these factors could result in an inability to obtain approval or delay their receipt. In addition, the Antitrust Division of the Department of Justice conducts a concurrent competitive review of the mergers to analyze each merger’s competitive effects and determine whether either merger would result in a violation of antitrust laws.

If Prosperity is not successful in obtaining the required regulatory approvals for either merger, the applicable merger will not be completed. Even if such regulatory approval is received, the timing of that regulatory approval could result in certain closing conditions of one or both of the mergers not being satisfied or in a delay in the consummation of one or both of the mergers. Furthermore, these regulators may impose conditions on the completion of the mergers or the bank mergers or require changes to the terms of the mergers or the bank mergers. Such conditions or changes could have the effect of delaying or preventing completion of the mergers or the bank mergers or imposing additional costs on or limiting the revenues of the combined company following the mergers and the bank mergers, any of which might have an adverse effect on the combined company following the mergers. See “The Mergers—Regulatory Approvals Required for the Mergers” beginning on page 87.

The consummation of the respective mergers is also subject to other conditions precedent as set forth in the respective reorganization agreements. Those conditions precedent include, among others, the approval of the respective mergers by First Bancshares’ shareholders and Lone Star’s shareholders, respectively, there being no material adverse change with respect to First Bancshares or Lone Star, respectively, on the one hand, or Prosperity, on the other hand, and various other closing conditions. If a condition to either party’s obligation to consummate the applicable merger is not satisfied or waived, the transaction would not be consummated or its consummation could be delayed. See “The Reorganization Agreements—Conditions to Completion of the Mergers” beginning on page 93 for a discussion of the conditions to the completion of the mergers.

Prosperity, First Bancshares and Lone Star will be subject to business uncertainties and contractual restrictions while the mergers are pending.

Uncertainty about the effect of the mergers on employees and customers may have an adverse effect on the parties to each merger. Uncertainties surrounding the mergers may impair the ability of one or more of Prosperity, Prosperity Bank, First Bancshares, FirstCapital Bank, Lone Star and Lone Star Bank to attract, retain and motivate key personnel until the respective mergers are completed, and could cause customers and others that deal with any of the banks to seek to change their existing business relationships with such bank. In addition, the respective reorganization agreements restrict First Bancshares and FirstCapital Bank, and Lone Star and Lone Star Bank, respectively, from taking specified actions until the respective merger occurs without Prosperity’s consent. These restrictions may prevent First Bancshares and FirstCapital Bank, or Lone Star and Lone Star Bank, respectively, from pursuing attractive business opportunities that may arise prior to the respective merger’s completion.

Certain of the directors and executive officers of First Bancshares and Lone Star have interests in the applicable merger that may be different from the interests of First Bancshares shareholders and Lone Star shareholders, respectively.

The shareholders of First Bancshares and Lone Star should be aware that some of the directors and executive officers of First Bancshares or Lone Star, as applicable, have interests in the applicable merger that may be different from, or in addition to, the interests of First Bancshares shareholders and Lone Star shareholders, respectively. The First Bancshares board of directors and the Lone Star board of directors, as applicable, were aware of these interests and considered them, among other matters, in approving the First Bancshares reorganization agreement and the Lone Star reorganization agreement, respectively, and the transactions contemplated by the applicable reorganization agreement and recommending to the First Bancshares shareholders and Lone Star shareholders, respectively, that they vote to approve the applicable merger proposal. These interests are described in more detail in the sections entitled “The First Bancshares Merger—Financial Interests of First Bancshares’ Directors and Executive Officers in the First Bancshares Merger” beginning on page 64 and “The Lone Star Merger—Financial Interests of Lone Star’s Directors and Executive Officers in the Lone Star Merger” beginning on page 83.

The opinions of the respective financial advisors to the First Bancshares board of directors and the Lone Star board of directors prior to the signing of the applicable reorganization agreement will not reflect changes in circumstances after the respective dates of the opinions.

The First Bancshares board of directors received a written opinion from Stephens dated October 10, 2022, that, as of such date and based upon and subject to the factors and assumptions set forth in its opinion, the merger consideration to be paid to the holders of First Bancshares common stock in the First Bancshares merger was fair, from a financial point of view, to such holders, which is attached hereto as Appendix G to this proxy statement/prospectus. The Lone Star board of directors received a written opinion from Stephens, dated October 7, 2022, that, as of such date and based upon and subject to the factors and assumptions set forth in its opinion, the merger consideration to be paid to the holders of Lone Star common stock in the Lone Star merger was fair, from a financial point of view, to such holders, which is attached as Appendix H to this proxy statement/prospectus. For a description of these opinions, see the sections entitled “The First Bancshares Merger—Opinion of First Bancshares’ Financial Advisor” beginning on page 54 and “The Lone Star Merger—Opinion of Lone Star’s Financial Advisor” beginning on page 73. Such opinions speak only as of the time such opinions were rendered, have not been updated as of the date of this proxy statement/prospectus and will not be updated at, or prior to, the time of the completion of the mergers. Changes in the operations and prospects of Prosperity, First Bancshares or Lone Star, general market and economic conditions and other factors that may be beyond the control of Prosperity, First Bancshares and Lone Star may alter the value of Prosperity, First Bancshares or Lone Star or the prices of shares of Prosperity common stock, First Bancshares common stock or Lone Star common stock by the time the mergers are completed. Further, the opinions regarding the First Bancshares merger and the Lone Star merger, respectively, do not take the other merger transaction into consideration. For a description of the other factors considered by the First Bancshares board of directors in determining to approve the First Bancshares merger and the Lone Star board of directors in determining to approve the Lone Star merger, see the sections entitled “The First Bancshares Merger—First Bancshares’ Reasons for the First Bancshares Merger and Recommendation of the First Bancshares Board of Directors” beginning on page 51 and “The Lone Star Merger—Lone Star’s Reasons for the Lone Star Merger and Recommendation of the Lone Star Board of Directors” beginning on page 70.

The respective reorganization agreements limit First Bancshares’ and Lone Star’s ability to pursue alternative acquisition proposals and require them to pay termination fees of approximately $13.7 million and approximately $9.1 million, respectively, under certain circumstances.

The reorganization agreements prohibit First Bancshares and Lone Star, respectively, from soliciting, knowingly encouraging or facilitating, initiating or participating in negotiations or discussions with respect to

certain alternative acquisition proposals with any third party, subject to exceptions set forth in the respective reorganization agreements. See “The Reorganization Agreements—No Solicitation” beginning on page 99. The reorganization agreements also provide that First Bancshares and Lone Star, respectively, must pay to Prosperity a termination fee in the amount of approximately $13.7 million and approximately $9.1 million, respectively, if the applicable reorganization agreement is terminated for certain reasons, including circumstances involving a change in recommendation by the First Bancshares board of directors or the Lone Star board of directors, respectively. These provisions might discourage a potential competing acquirer that might have an interest in acquiring all or a significant part of First Bancshares or Lone Star from considering or proposing such an acquisition. See “The Reorganization Agreements—Termination Fees and Effect of Termination” beginning on page 104.

If the mergers are not completed, Prosperity, First Bancshares and Lone Star will have incurred substantial expenses without realizing the expected benefits of the respective mergers.

Each of Prosperity, First Bancshares and Lone Star has incurred and will incur substantial expenses in connection with the negotiation and completion of the transactions contemplated by the respective reorganization agreements, as well as the costs and expenses of filing, printing and mailing this proxy statement/prospectus and all filing and other fees paid to the SEC and fees to other regulators in connection with the respective mergers. If either merger is not completed, Prosperity and the applicable party would have to recognize these and other expenses without realizing the expected benefits of the applicable merger.

Termination of the reorganization agreements could negatively impact First Bancshares, Lone Star or Prosperity.

There may be various negative consequences if either or both of the reorganization agreements are terminated. For example, First Bancshares’, Lone Star’s or Prosperity’s businesses may have been impacted adversely by the failure to pursue other beneficial opportunities due to the focus of management on the applicable merger, without realizing any of the anticipated benefits of completing such merger. Additionally, if the respective reorganization agreement is terminated, the market price of First Bancshares’, Lone Star’s and/or Prosperity’s common stock could decline to the extent that the current market prices reflect a positive market assumption that the applicable merger will be completed. If the First Bancshares reorganization agreement is terminated under certain circumstances, First Bancshares would be required to pay to Prosperity a termination fee of approximately $13.7 million. If the Lone Star reorganization agreement is terminated under certain circumstances, Lone Star would be required to pay to Prosperity a termination fee of approximately $9.1 million.

Risks Relating to the Combined Company’s Business Following the Mergers

Integrating FirstCapital Bank and Lone Star Bank, respectively, into Prosperity Bank’s operations may be more difficult, costly or time-consuming than Prosperity expects.

Prosperity Bank, FirstCapital Bank and Lone Star Bank have operated and, until the respective mergers are completed, will continue to operate, independently. Accordingly, the process of integrating FirstCapital Bank’s and Lone Star Bank’s respective operations into Prosperity Bank’s operations could result in the disruption of operations, the loss of FirstCapital Bank or Lone Star Bank customers and employees and make it more difficult to achieve the intended benefits of the respective mergers. Inconsistencies between the standards, controls, procedures and policies of Prosperity Bank and those of FirstCapital Bank and Lone Star Bank could adversely affect Prosperity Bank’s ability to maintain relationships with current customers and employees of FirstCapital Bank and Lone Star Bank, respectively, if and when the respective mergers are completed.

As with any merger of banking institutions, business disruptions may occur that may cause Prosperity Bank to lose customers or may cause FirstCapital Bank’s or Lone Star Bank’s respective customers to withdraw their deposits from FirstCapital Bank or Lone Star Bank, respectively, prior to the respective merger’s consummation

and from Prosperity Bank thereafter. The realization of the anticipated benefits of the respective mergers may depend in large part on Prosperity’s ability to integrate FirstCapital Bank’s and Lone Star Bank’s respective operations into Prosperity Bank’s operations, and to address differences in business models and cultures. If Prosperity is unable to integrate the operations of First Bancshares and FirstCapital Bank, or Lone Star and Lone Star Bank, into Prosperity’s and Prosperity Bank’s operations successfully and on a timely basis, some or all of the expected benefits of the respective mergers may not be realized. Difficulties encountered with respect to such matters could result in an adverse effect on the financial condition, results of operations, capital, liquidity or cash flows of Prosperity Bank and Prosperity.

Prosperity may fail to realize the cost savings anticipated from the mergers.

Although Prosperity anticipates that it would realize certain cost savings as to the operations of First Bancshares and FirstCapital Bank, and Lone Star and Lone Star Bank, and otherwise from the respective mergers if and when the operations of First Bancshares and FirstCapital Bank, and Lone Star and Lone Star Bank, respectively, are fully integrated into Prosperity’s and Prosperity Bank’s operations, it is possible that Prosperity may not realize all of the cost savings that Prosperity has estimated it can realize from the respective mergers. For example, for a variety of reasons, Prosperity may be required to continue to operate or maintain some facilities or support functions that are currently expected to be combined or reduced as a result of the mergers. Prosperity’s realization of the estimated cost savings also will depend on Prosperity’s ability to combine the operations of Prosperity and Prosperity Bank with the operations of First Bancshares and FirstCapital Bank, and Lone Star and Lone Star Bank, respectively, in a manner that permits those cost savings to be realized. If Prosperity is not able to integrate the operations of First Bancshares and FirstCapital Bank, and Lone Star and Lone Star Bank, into Prosperity’s and Prosperity Bank’s operations successfully and to reduce the combined costs of conducting the integration operations of the banks, the anticipated cost savings may not be fully realized, if at all, or may take longer to realize than expected. Prosperity’s failure to realize those cost savings could materially adversely affect Prosperity’s financial condition, results of operations, capital, liquidity or cash flows.

First Bancshares shareholders and Lone Star shareholders will have a reduced ownership and voting interest in Prosperity after the respective mergers than they now have in First Bancshares and Lone Star, respectively, and will exercise less influence over Prosperity’s management than they now exercise over the management of First Bancshares and Lone Star, respectively.

First Bancshares’ shareholders currently have the right to vote in the election of the board of directors of First Bancshares and on other matters affecting First Bancshares, and Lone Star’s shareholders currently have the right to vote in the election of the board of directors of Lone Star and on other matters affecting Lone Star. The respective mergers will transfer control of the operations of First Bancshares and Lone Star, respectively, to Prosperity and to the shareholders of Prosperity. When the respective mergers occur, each First Bancshares shareholder and each Lone Star shareholder will become a shareholder of Prosperity with a percentage ownership of Prosperity significantly smaller than such shareholder’s percentage ownership of First Bancshares or Lone Star, respectively, immediately prior to the respective merger. If the mergers are both completed, existing Prosperity shareholders would own approximately [ ]% of Prosperity common stock immediately following completion of the mergers, former Lone Star shareholders would own approximately [ ]% and former First Bancshares shareholders would own approximately [ ]%. If the First Bancshares merger is completed, but the Lone Star merger is not completed, existing Prosperity shareholders and First Bancshares shareholders would own approximately [ ]% and [ ]%, respectively, of Prosperity common stock upon completion of the First Bancshares merger. If the Lone Star merger is completed, but the First Bancshares merger is not completed, existing Prosperity shareholders and Lone Star shareholders would own approximately [ ]% and [ ]%, respectively, of Prosperity common stock upon completion of the Lone Star merger. As a result, First Bancshares shareholders and Lone Star shareholders will have less influence on the management and policies of Prosperity than they now have on the management and policies of First Bancshares and Lone Star, respectively.

Risks Relating to an Investment in Prosperity Common Stock

The market price of Prosperity common stock after the respective mergers may be affected by factors different from those affecting the shares of First Bancshares, Lone Star or Prosperity currently.

Upon completion of the respective mergers, holders of Lone Star common stock and of First Bancshares common stock will become holders of Prosperity common stock. Prosperity’s business differs in important respects from that of First Bancshares and Lone Star, and, accordingly, the results of operations of the combined company and the market price of Prosperity common stock after the completion of the respective mergers may be affected by factors different from those currently affecting the independent results of operations of each of First Bancshares, Lone Star and Prosperity.

The shares of Prosperity common stock to be received by First Bancshares shareholders and Lone Star shareholders as a result of the First Bancshares merger and Lone Star merger, respectively, will have different rights than the shares of First Bancshares common stock and Lone Star common stock, respectively, and in some cases may be less favorable.

The rights associated with First Bancshares common stock and Lone Star common stock are different from the rights associated with Prosperity common stock. In some cases, the rights associated with the Prosperity common stock may be less favorable to shareholders than those associated with the First Bancshares common stock and Lone Star common stock. For example, holders of First Bancshares common stock and Lone Star common stock currently elect each member of their respective board of directors at each annual meeting of the First Bancshares shareholders and Lone Star shareholders, respectively. Upon consummation of the First Bancshares merger and the Lone Star merger, the holders of Lone Star common stock and the holders of First Bancshares common stock, respectively, will hold Prosperity common stock that provides that the members of only one of three classes of directors are elected at each annual meeting of Prosperity shareholders, which could have an anti-takeover effect and may delay, discourage or prevent an attempted acquisition or change in control of Prosperity. See “Comparison of Rights of Shareholders of Prosperity and First Bancshares” beginning on page 125 and “Comparison of Rights of Shareholders of Prosperity and Lone Star” beginning on page 130 for a more detailed description of the shareholder rights of each of Prosperity, First Bancshares and Lone Star.

THE FIRST BANCSHARES SPECIAL MEETING

This section contains information for First Bancshares shareholders about the First Bancshares special meeting. First Bancshares is mailing or otherwise delivering this proxy statement/prospectus to you, as a First Bancshares shareholder, on or about [ ], 2023. This proxy statement/prospectus is also being delivered to First Bancshares shareholders as Prosperity’s prospectus for its offering of Prosperity common stock in connection with the First Bancshares merger. This proxy statement/prospectus is accompanied by a notice of the First Bancshares special meeting and a proxy that the First Bancshares board of directors is soliciting for use by First Bancshares shareholders at the First Bancshares special meeting and at any adjournments or postponements of the First Bancshares special meeting. References to “you” and “your” in this section are to First Bancshares shareholders.

Date, Time and Place

The First Bancshares special meeting will be held virtually on [ ], 2023 at [ ], Central Time. In order to attend the First Bancshares special meeting, First Bancshares shareholders must register before the special meeting date from a computer, tablet or smartphone by accessing the following web address: [https://fcbtexas.com/FBOTMeeting]. There will not be a physical meeting to attend in person.

Matters to Be Considered

At the First Bancshares special meeting, you will be asked to consider and vote upon the following proposals:

First Bancshares merger proposal: to approve the First Bancshares reorganization agreement and the transactions contemplated thereby, including the First Bancshares merger; and

First Bancshares adjournment proposal: to adjourn the First Bancshares special meeting to a later date or dates if the board of directors of First Bancshares determines it is necessary or appropriate, including adjournments to permit the solicitation of additional proxies in favor of the First Bancshares merger proposal.

Completion of the First Bancshares merger is conditioned on, among other things, the approval of the reorganization agreement by the requisite First Bancshares shareholder vote, as well as the receipt of all required regulatory approvals.

Recommendation of the First Bancshares Board of Directors

The First Bancshares board of directors has unanimously approved the First Bancshares reorganization agreement and determined that the First Bancshares merger and the other transactions contemplated by the First Bancshares reorganization agreement are in the best interests of First Bancshares and its shareholders.

Accordingly, the First Bancshares board of directors recommends that First Bancshares shareholders vote as follows:

“FOR” the First Bancshares merger proposal; and

“FOR” the First Bancshares adjournment proposal.

Holders of First Bancshares common stock should carefully read this proxy statement/prospectus, including any documents incorporated by reference, and the appendices in their entirety for more detailed information concerning the First Bancshares merger and the transactions contemplated by the First Bancshares reorganization agreement.

Completion of the First Bancshares merger is conditioned upon the approval of the First Bancshares merger proposal, but is not conditioned upon the approval of the First Bancshares adjournment proposal. Neither the closing of the First Bancshares merger nor the closing of the Lone Star merger is conditioned upon closing of the other merger.

First Bancshares Record Date; Shareholders Entitled to Vote

The record date for the First Bancshares special meeting is [ ], 2023, or the “First Bancshares record date.” Only record holders of shares of First Bancshares common stock at the close of business on the First Bancshares record date are entitled to notice of, to attend and to vote at, the First Bancshares special meeting or any adjournment or postponement thereof. At the close of business on the First Bancshares record date, the only outstanding voting securities of Lone Star were shares of common stock, and [ ] shares of First Bancshares common stock were issued and outstanding.

Each share of First Bancshares common stock outstanding on the First Bancshares record date is entitled to one vote on each proposal.

Voting by First Bancshares’ Directors and Executive Officers

At the close of business on the record date for the First Bancshares special meeting, First Bancshares directors and executive officers and their affiliates were entitled to vote approximately [ ] shares of First Bancshares common stock, or approximately [ ]% of the shares of First Bancshares common stock outstanding on that date.

First Bancshares currently expects that the shares of First Bancshares common stock beneficially owned by its directors and executive officers will be voted in favor of the First Bancshares merger proposal and the First Bancshares adjournment proposal. In connection with the First Bancshares reorganization agreement, each of the directors and certain executive officers of First Bancshares, in their capacities as individuals, have separately entered into First Bancshares voting agreements pursuant to which they agreed to vote their beneficially owned shares of First Bancshares common stock in favor of the First Bancshares merger proposal and certain related matters and against alternative transactions. For further information, see the section entitled “The Reorganization Agreements—Voting Agreements” beginning on page 107.

Quorum and Adjournment

No business may be transacted at the First Bancshares special meeting unless a quorum is present. First Bancshares shareholders who hold shares representing at least a majority of the shares of First Bancshares capital stock outstanding and entitled to vote at the First Bancshares special meeting must be present in person or represented by proxy to constitute a quorum.

If a quorum is not present, then the First Bancshares special meeting may be adjourned to allow for the solicitation of additional proxies. The First Bancshares special meeting may be adjourned by the holders of a majority in number of the shares of stock present in person or represented by proxy and entitled to vote, or by the chairman of the meeting without a vote of the shareholders.

No notice of an adjourned First Bancshares special meeting need be given if the time, date and place thereof are announced at the First Bancshares special meeting. At any adjourned First Bancshares special meeting, all proxies will be voted in the same manner as they would have been voted at the original convening of the First Bancshares special meeting, except for any proxies that have been effectively revoked or withdrawn prior to the adjourned First Bancshares special meeting.

All shares of First Bancshares common stock represented at the First Bancshares special meeting, including shares of First Bancshares common stock that are represented but that vote to abstain and broker nonvotes, will be treated as present for purposes of determining the presence or absence of a quorum.

Participation in the First Bancshares special meeting by electronic means in accordance with the instructions given above will constitute the presence in person at the First Bancshares special meeting, except where such shareholder participates in the meeting for the express purpose of objecting to the transaction of business on the ground that the meeting is not lawfully called or convened.

Required Vote; Treatment of Abstentions; Broker Non-Votes and Failure to Vote

The required votes to approve the First Bancshares proposals are as follows:

Approval of the First Bancshares merger proposal requires the affirmative vote of holders of at least two-thirds of the outstanding shares of First Bancshares common stock entitled to vote on the proposal. If you are a First Bancshares shareholder and mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the First Bancshares special meeting, or if you fail to instruct your bank, broker or other nominee how to vote with respect to the First Bancshares merger proposal, it will have the same effect as a vote against the proposal.

Approval of the First Bancshares adjournment proposal requires the affirmative vote of holders of at least a majority of the outstanding shares of First Bancshares common stock entitled to vote on the proposal who are present in person or represented by proxy at the First Bancshares special meeting. A quorum is not required for a vote on the First Bancshares adjournment proposal. If you are a First Bancshares shareholder who is present in person or represented by proxy at the First Bancshares special meeting and you mark “ABSTAIN” on your proxy, fail to vote on the First Bancshares adjournment proposal or fail to instruct your bank, broker or other nominee how to vote with respect to the First Bancshares adjournment proposal, it will have the same effect as a vote against the proposal. If you are not present in person or represented by proxy at the First Bancshares special meeting, it will have no effect on the First Bancshares adjournment proposal.

Voting and Revocation of Proxies

Proxies, in the form enclosed, which are properly executed and returned and not subsequently revoked, will be voted in accordance with the instructions indicated on the proxies. Any properly executed proxy on which voting instructions are not specified will be voted “FOR” the First Bancshares merger proposal and “FOR” the First Bancshares adjournment proposal. The proxy also grants authority to the persons designated in such proxy to vote in accordance with their own judgment if an unscheduled matter is properly brought before the First Bancshares special meeting.

In order to attend and vote at the First Bancshares special meeting, please register before the special meeting date from your computer, tablet or smartphone by accessing the following link: [https://fcbtexas.com/FBOTMeeting]. After registering, you will receive a confirmation email containing information about joining the First Bancshares special meeting virtually. A fillable form will be provided online at the beginning of the First Bancshares special meeting for First Bancshares shareholders to vote during the meeting, which will supersede any previously submitted proxy.

A record holder of First Bancshares common stock may revoke a previously delivered proxy before it is voted at the special meeting by:

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delivering a written notice of revocation to First Bancshares’ transfer agent, Manhattan Transfer Registrar Co., by facsimile at (631) 209-8143 or by email at dcarlo@mtrco.com;

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by completing, signing, dating and returning a proxy with a later date in accordance with the instructions on the enclosed proxy; or

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attending and voting in person virtually at the First Bancshares special meeting using the fillable form provided online at the beginning of the meeting.

All written notices of revocation and other communications with respect to revocation or proxies must be sent to: Manhattan Transfer Registrar Co. by facsimile at (631) 209-8143 or email at dcarlo@mtrco.com. If you

hold your shares in street name with a bank or broker, you must contact such bank or broker for instructions as to how to revoke your proxy.

Dissenters’ Rights

First Bancshares shareholders are entitled to dissenters’ rights with respect to the First Bancshares merger proposal. These dissenters’ rights are conditioned on strict compliance with requirements of the applicable provisions of the Texas Business Organizations Code. Please see the section entitled “The Mergers—Dissenters’ Rights of Appraisal,” and the full text of the applicable provisions of the Texas Business Organizations Code, which are reproduced in full in Appendix I to this proxy statement/prospectus.

Solicitation of Proxies

The First Bancshares board of directors is soliciting proxies for the First Bancshares special meeting from holders of shares of First Bancshares common stock entitled to vote at such special meeting. First Bancshares is responsible for its expenses incurred in preparing, assembling, printing, and mailing this proxy statement/prospectus. Proxies will be solicited through the mail. Additionally, directors and officers of First Bancshares intend to solicit proxies personally or by telephone or other means of communication. The directors and officers of First Bancshares will not be additionally compensated for any such solicitation. First Bancshares will reimburse banks, brokers and other custodians, nominees and fiduciaries for their reasonable expenses in forwarding the proxy materials to beneficial owners.

Assistance

If you need assistance in completing your proxy, have questions regarding the First Bancshares special meeting, or would like additional copies of this proxy statement/prospectus, please contact Robin Richey, telephone: (432) 687-9102, email: rrichey@fcbtexas.com.

THE LONE STAR SPECIAL MEETING

This section contains information for Lone Star shareholders about the Lone Star special meeting. Lone Star is mailing or otherwise delivering this proxy statement/prospectus to you, as a Lone Star shareholder, on or about [ ], 2023. This proxy statement/prospectus is also being delivered to Lone Star shareholders as Prosperity’s prospectus for its offering of Prosperity common stock in connection with the Lone Star merger. This proxy statement/prospectus is accompanied by a notice of the Lone Star special meeting and a proxy that the Lone Star board of directors is soliciting for use by Lone Star shareholders at the Lone Star special meeting and at any adjournments or postponements of the Lone Star special meeting. References to “you” and “your” in this section are to Lone Star shareholders.

Date, Time and Place

The Lone Star special meeting will be held on [ ], 2023 at [ ], Central Time, at 6220 Milwaukee Avenue, Lubbock, Texas 79424.

Matters to Be Considered

At the Lone Star special meeting, you will be asked to consider and vote upon the following proposals:

Lone Star merger proposal: to approve the Lone Star reorganization agreement and the transactions contemplated thereby, including the Lone Star merger; and

Lone Star adjournment proposal: to adjourn the Lone Star special meeting to a later date or dates, if the board of directors of Lone Star determines it is necessary or appropriate, including adjournments to permit the solicitation of additional proxies in favor of the Lone Star merger proposal.

Completion of the Lone Star merger is conditioned on, among other things, the approval of the reorganization agreement by the requisite Lone Star shareholder vote, as well as the receipt of all required regulatory approvals.

Recommendation of the Lone Star Board of Directors

The Lone Star board of directors has unanimously approved the Lone Star reorganization agreement and determined that the Lone Star merger and the other transactions contemplated by the Lone Star reorganization agreement are in the best interests of Lone Star and its shareholders.

Accordingly, the Lone Star board of directors recommends that Lone Star shareholders vote:

“FOR” the Lone Star merger proposal; and

“FOR” the Lone Star adjournment proposal.

Holders of Lone Star common stock should carefully read this proxy statement/prospectus, including any documents incorporated by reference, and the appendices in their entirety for more detailed information concerning the Lone Star merger and the transactions contemplated by the Lone Star reorganization agreement.

Completion of the Lone Star merger is conditioned upon the approval of the Lone Star merger proposal, but is not conditioned upon the approval of the Lone Star adjournment proposal. Neither the closing of the Lone Star merger nor the closing of the First Bancshares merger is conditioned upon closing of the other merger.

Lone Star Record Date; Shareholders Entitled to Vote

The record date for the Lone Star special meeting is [ ], 2023, or the “Lone Star record date.” Only record holders of shares of Lone Star common stock at the close of business on the Lone Star record date are entitled to

notice of, to attend and to vote at, the Lone Star special meeting or any adjournment or postponement thereof. At the close of business on the Lone Star record date, the only outstanding voting securities of Lone Star were shares of common stock, and [ ] shares of Lone Star common stock were issued and outstanding.

Each share of Lone Star common stock outstanding on the Lone Star record date is entitled to one vote on each proposal.

Voting by Lone Star’s Directors and Executive Officers

At the close of business on the record date for the Lone Star special meeting, Lone Star directors and executive officers and their affiliates were entitled to vote approximately [ ] shares of Lone Star common stock, or approximately [ ]% of the shares of Lone Star common stock outstanding on that date.

Lone Star currently expects that the shares of Lone Star common stock beneficially owned by its directors and executive officers will be voted in favor of the Lone Star merger proposal and the Lone Star adjournment proposal. In connection with the Lone Star reorganization agreement, each of the directors, certain executive officers and certain shareholders of Lone Star, in their capacities as individuals, have separately entered into Lone Star voting agreements pursuant to which they agreed to vote their beneficially owned shares of Lone Star common stock in favor of the Lone Star merger proposal and certain related matters and against alternative transactions. For further information, see the section entitled “The Reorganization Agreements—Voting Agreements” beginning on page 107.

Quorum and Adjournment

No business may be transacted at the Lone Star special meeting unless a quorum is present. Lone Star shareholders who hold shares representing at least a majority of the shares of Lone Star capital stock outstanding and entitled to vote at the Lone Star special meeting must be present in person or represented by proxy to constitute a quorum.

If a quorum is not present, then the Lone Star special meeting may be adjourned to allow for the solicitation of additional proxies. The Lone Star special meeting may be adjourned by the holders of a majority in number of the shares of stock present in person or represented by proxy and entitled to vote, or by the chairman of the meeting without a vote of the shareholders.

No notice of an adjourned Lone Star special meeting need be given unless the adjournment is for more than 30 days or, after the adjournment, a new record date is fixed for the adjourned Lone Star special meeting, in which case a notice of the adjourned Lone Star special meeting shall be given to each Lone Star shareholder of record entitled to vote at the Lone Star special meeting. At any adjourned Lone Star special meeting, all proxies will be voted in the same manner as they would have been voted at the original convening of the Lone Star special meeting, except for any proxies that have been effectively revoked or withdrawn prior to the adjourned Lone Star special meeting.

All shares of Lone Star common stock represented at the Lone Star special meeting, including shares of Lone Star common stock that are represented but that vote to abstain and broker nonvotes, will be treated as present for purposes of determining the presence or absence of a quorum.

Required Vote; Treatment of Abstentions; Broker Non-Votes and Failure to Vote

Approval of the Lone Star merger proposal requires the affirmative vote of holders of at least two-thirds of the outstanding shares of Lone Star common stock entitled to vote on the proposal. If you are a Lone Star shareholder and mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the Lone Star special meeting, or if you fail to instruct your bank, broker or other nominee how to vote with respect to the Lone Star merger proposal, it will have the same effect as a vote against the proposal.

Approval of the Lone Star adjournment proposal requires the affirmative vote of holders of at least a majority of the outstanding shares of Lone Star common stock entitled to vote on the proposal who are present in person or represented by proxy at the Lone Star special meeting. A quorum is not required for a vote on the Lone Star adjournment proposal. If you are a Lone Star shareholder who is present in person or represented by proxy at the Lone Star special meeting and you mark “ABSTAIN” on your proxy, fail to vote on the Lone Star adjournment proposal or fail to instruct your bank, broker or other nominee how to vote with respect to the Lone Star adjournment proposal, it will have the same effect as a vote against the proposal. If you are not present in person or represented by proxy at the Lone Star special meeting, it will have no effect on the Lone Star adjournment proposal.

Voting and Revocation of Proxies

Proxies, in the form enclosed, which are properly executed and returned and not subsequently revoked, will be voted in accordance with the instructions indicated on the proxies. Any properly executed proxy on which voting instructions are not specified will be voted “FOR” the Lone Star merger proposal and “FOR” the Lone Star adjournment proposal. The proxy also grants authority to the persons designated in such proxy to vote in accordance with their own judgment if an unscheduled matter is properly brought before the Lone Star special meeting.

A holder of Lone Star common stock may revoke a previously delivered proxy before it is voted at the special meeting by:

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delivering a written notice of revocation to the LaNell Martindale, Senior Vice President of Lone Star;

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executing a proxy bearing a later date and delivering that proxy to LaNell Martindale, Senior Vice President of Lone Star, that is received prior to the Lone Star special meeting; or

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attending and voting in person at the Lone Star special meeting.

All written notices of revocation and other communications with respect to revocation or proxies must be sent to: Lone Star State Bancshares, Inc., 6220 Milwaukee Avenue, Lubbock, Texas 79424, Attention: LaNell Martindale, Senior Vice President. If you hold your shares in street name with a bank or broker, you must contact such bank or broker for instructions as to how to revoke your proxy.

Dissenters’ Rights

Lone Star shareholders are entitled to dissenters’ rights with respect to the Lone Star merger proposal. These dissenters’ rights are conditioned on strict compliance with requirements of the applicable provisions of the Texas Business Organizations Code. Please see the section entitled “The Mergers—Dissenters’ Rights of Appraisal,” and the full text of the applicable provisions of the Texas Business Organizations Code, which are reproduced in full in Appendix I to this proxy statement/prospectus.

Participants in the Lone Star State Bancshares, Inc. and Subsidiaries Employee Stock Ownership Plan

Each participant in the Lone Star State Bancshares, Inc. and Subsidiaries Employee Stock Ownership Plan, or the “Lone Star ESOP,” is entitled to direct the trustee of the plan on how to vote the shares of Lone Star common stock allocated to his or her account under the Lone Star ESOP. If a participant properly executes the voting instruction card distributed by the trustee of the Lone Star ESOP, the trustee will vote the participant’s shares in accordance with the instructions. Where properly executed voting instruction cards are returned to the trustee with no specific instruction as to how to vote at the Lone Star special meeting, or in the event a participant fails to give timely voting instructions to the trustee with respect to the voting of the Lone Star common stock that is allocated to his or her Lone Star ESOP account, the trustee will vote the shares as directed by the administrator of the Lone Star ESOP. The trustee will vote the shares of Lone Star common stock held in the

Lone Star ESOP but not allocated to any participant’s account in the same proportion as directed by the participants who directed the trustee as to the manner of voting their allocated shares in the ESOP with respect to each proposal.

Solicitation of Proxies

The Lone Star board of directors is soliciting proxies for the Lone Star special meeting from holders of shares of Lone Star common stock entitled to vote at such special meeting. Lone Star is responsible for its expenses incurred in preparing, assembling, printing, and mailing this proxy statement/prospectus. Proxies will be solicited through the mail. Additionally, directors, officers and employees of Lone Star may also solicit proxies personally or by telephone or other means of communication. Lone Star will not pay any additional or special compensation to these directors, officers or employees for these activities, but may reimburse them for out-of-pocket expenses. Lone Star will reimburse banks, brokers and other custodians, nominees and fiduciaries for their reasonable out-of-pocket expenses in forwarding the proxy materials to beneficial owners.

Assistance

If you need assistance in completing your proxy, have questions regarding the Lone Star special meeting, or would like additional copies of this proxy statement/prospectus, please contact Alan Lackey, telephone: (806) 771-7717, email: alanlackey@lonestarwtx.com, or Melisa Roberts, telephone: (806) 771-7717, email: mroberts@lonestarwtx.com.

THE FIRST BANCSHARES MERGER

The following discussion contains material information regarding the First Bancshares merger. The discussion is subject to, and qualified in its entirety by reference to, the First Bancshares reorganization agreement, which is attached to this proxy statement/prospectus as Appendix A and is incorporated by reference into this proxy statement/prospectus. The following is not intended to provide factual information about the parties or any of their respective subsidiaries or affiliates. This discussion does not purport to be complete and may not contain all of the information about the First Bancshares merger that is important to you. We urge you to read the First Bancshares reorganization agreement carefully and in its entirety, as it is the legal document governing the First Bancshares merger.

Terms of the First Bancshares Merger

Each of the Prosperity board of directors and the First Bancshares board of directors approved the First Bancshares reorganization agreement. The First Bancshares reorganization agreement provides that, among other things, First Bancshares will merge with and into Prosperity, with Prosperity as the surviving corporation in the merger. Immediately following the First Bancshares merger, FirstCapital Bank will merge with and into Prosperity Bank, with Prosperity Bank as the surviving bank.

If the First Bancshares reorganization agreement is approved by the First Bancshares shareholders and the First Bancshares merger is completed, all shares of First Bancshares common stock issued and outstanding immediately prior to the First Bancshares effective time will be converted into an aggregate of 3,583,370 shares of Prosperity common stock and $93,422,648 in cash, less any amounts paid at closing with respect to outstanding equity awards, as set forth in the First Bancshares reorganization agreement. Additionally, the aggregate First Bancshares cash consideration will be reduced on a dollar-for-dollar basis if First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is less than $204,000,000 at closing of the First Bancshares merger. Because of the possibility of an adjustment to the First Bancshares cash consideration, you will not know the exact amount of cash you will receive in connection with the First Bancshares merger when you vote on the First Bancshares reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each First Bancshares shareholder will receive.

For illustration purposes only, if the First Bancshares merger occurs and assuming at the closing that (i) there are [ ] shares of First Bancshares common stock issued and outstanding, (ii) there are [ ] unexercised options to purchase shares of First Bancshares common stock with a weighted average exercise price of $[ ], (iii) First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is equal to or greater than $204,000,000, and (iv) the price per share of Prosperity common stock received in the First Bancshares merger is equal to $[ ], which was the closing price per share of Prosperity common stock on [ ], 2023, then holders of First Bancshares common stock will receive [ ] shares of Prosperity common stock with a value of $[ ] (before adjusting for fractional shares) and $[ ] in cash for each share they own, for an aggregate implied value of $[ ] for each share of First Bancshares common stock.

First Bancshares shareholders are being asked to approve the First Bancshares reorganization agreement, including the First Bancshares merger and all transactions contemplated thereby. See the section entitled “The

Reorganization Agreements” beginning on page 89 for additional and more detailed information regarding the legal documents that govern the First Bancshares merger, including information about the conditions to consummation of the First Bancshares merger and the provisions for terminating or amending the First Bancshares reorganization agreement.

Background of the First Bancshares Merger

As part of the ongoing consideration and evaluation of First Bancshares’ long-term prospects and strategies, First Bancshares’ board of directors and senior management have regularly reviewed and assessed First Bancshares’ business strategies and objectives, including First Bancshares’ future prospects for earnings and asset growth as well as the viability of strategic growth opportunities potentially available to First Bancshares. From time to time, First Bancshares’ board of directors and senior management have reviewed and discussed First Bancshares’ long-term objectives and considered ways to enhance shareholder value and performance of the consolidated organization. These strategic discussions and reviews have focused on, among other things, prospects and developments in the financial services industry, the regulatory environment, the economy and the financial markets generally, and the implications of such developments both for financial institutions generally and for First Bancshares, in particular. These strategic discussions were part of the continuous efforts of First Bancshares to enhance value for its shareholders and deliver the best possible services to its customers and communities. This strategic review has also included assessment of ongoing consolidation in the financial services industry and the benefits and risks to First Bancshares and its shareholders of strategic combinations compared to the benefits and risks of continued operation as a stand-alone company. Factors assessed in connection with this review have included the benefits and risks of operating in existing and new markets, competition, potential expense and revenue synergies, regulatory requirements, the interest rate environment, scale and diversification, credit risk, market risk and the impacts of rapidly changing technology and the delivery channels for products and services.

In furtherance of the foregoing, in February 2022 the First Bancshares board of directors determined to explore the possibility of a strategic business combination, including the prospect of merging First Bancshares into a larger institution, and to identify potential strategic merger partners. After reviewing proposals from Stephens and another investment banking firm, First Bancshares engaged Stephens as its financial advisor in March 2022. Representatives of Stephens met with First Bancshares’ management team on March 14 and 15, 2022 to conduct a preliminary due diligence review of First Bancshares and to gather information that management believed to be necessary information for evaluating market factors affecting First Bancshares’ strategic objectives and making sound recommendations to the First Bancshares board of directors regarding the strategic direction of First Bancshares.

On April 26, 2022, representatives of Stephens met with the First Bancshares board of directors to discuss current market conditions, industry trends, potential merger partners and strategic business combination opportunities and the process for pursuing First Bancshares strategic objectives. At that meeting, the First Bancshares board of directors directed Stephens to contact a selected group of potential strategic partners.

On May 23, 2022, Kenneth L. Burgess, Jr., First Bancshares’ Chairman and Chief Executive Officer, Don Cosby, First Bancshares’ President, and representatives of Stephens met with a potential strategic partner. Following the initial meeting, the parties engaged in further preliminary discussions regarding a potential business combination, including discussions regarding the potential merits and risks of a combination between the institutions. After these initial discussions the parties declined to pursue a business combination.

On June 28, 2022, representatives of Stephens again met with the First Bancshares board of directors to discuss current market conditions, potential merger partners and potential strategic opportunities.

On July 12, 2022, representatives of Stephens met with members of Prosperity’s management team for an initial discussion of Prosperity’s interest in pursuing a transaction with First Bancshares. Prosperity indicated that

it would be interested in meeting First Bancshares’ management team and further discussing a potential strategic combination between the institutions.

On July 20, 2022, Mr. Burgess, Mr. Cosby and representatives of Stephens met with members of Prosperity’s management team and discussed preliminary terms of a strategic combination between the institutions, the potential merits, risks and viability of pursuing a combination, the anticipated benefits and challenges for completing a transaction and integrating business cultures, personnel matters and market considerations.

On July 29, 2022, Stephens received the initial letter of intent from Prosperity for a proposed acquisition of First Bancshares by Prosperity. On this date, Prosperity and First Bancshares also entered into a Non-Disclosure and Confidentiality Agreement pursuant to which the parties began sharing information for the purposes of their respective due diligence processes.

During the following week, members of First Bancshares’ management and Stephens, in consultation with First Bancshares’ legal counsel, Fenimore Kay Harrison LLP, or “Fenimore,” negotiated the terms of the letter of intent to reflect the interests of First Bancshares’ stakeholders in the proposed transaction. Throughout these negotiations, the parties negotiated certain economic and material terms of the proposed transaction.

On August 3, 2022, Prosperity delivered a revised letter of intent to Stephens reflecting the negotiations between the parties. After review and discussion, the M&A Committee of the First Bancshares board of directors approved the revised letter of intent and recommended it to the full board of directors, subject to certain counterproposals of the committee, which Stephens and First Bancshares management were instructed to negotiate with Prosperity.

On August 4, 2022, First Bancshares, along with Stephens and Fenimore, provided Prosperity with a revised letter of intent. Following further negotiations between the parties, Prosperity delivered a revised letter of intent to Stephens on August 5, 2022.

On August 8, 2022, the First Bancshares board of directors met to consider the revised letter of intent. The First Bancshares board of directors, in consultation with Stephens, discussed the terms of the revised letter of intent, the viability of a business combination with Prosperity as proposed in the revised letter of intent, the anticipated benefits and challenges related to the proposal and pursuing a transaction that would be in the best interests of First Bancshares’ customers, employees, communities and shareholders. After an in-depth discussion, the First Bancshares board of directors authorized management to execute and deliver the letter of intent and pursue a business combination with Prosperity as set forth in the letter of intent. On that same date, Mr. Burgess executed and delivered the letter to intent on behalf of First Bancshares to Prosperity.

During August and September 2022, Mr. Burgess, Mr. Cosby, other members of the First Bancshares management team and representatives of Stephens met several times with senior members of Prosperity’s management team to discuss various deal terms, due diligence matters and preliminary integration and personnel considerations.

During this same period, First Bancshares provided Prosperity with access to an electronic virtual data room to allow Prosperity to conduct a due diligence investigation of First Bancshares, including its results of operations, financial condition, loan portfolio and tax, litigation and other matters. During this same period, members of First Bancshares’ management team, together with First Bancshares’ advisors, conducted reverse due diligence of Prosperity and its operations.

Based on Prosperity’s due diligence investigation of First Bancshares, Prosperity proposed certain adjustments to the terms of the proposed transaction. On September 16, 2022, the First Bancshares board of directors met and determined to move forward with the proposed business combination based on Prosperity’s revised terms.

On September 27, 2022, First Bancshares and Fenimore received an initial draft of the First Bancshares reorganization agreement prepared by Prosperity and its legal counsel, Bracewell LLP. Until the First Bancshares reorganization agreement was signed on October 10, 2022, First Bancshares and Prosperity, in consultation with their respective legal counsel, exchanged several drafts of, and negotiated the terms of, the First Bancshares reorganization agreement and related ancillary documents and agreements (including disclosure schedules, voting agreements, and support agreements and releases with certain directors and officers, and employment agreements with certain officers of First Bancshares). In such negotiations, First Bancshares and its advisors negotiated for terms that reflected the interests of First Bancshares’ stakeholders in the transaction, were consistent with best market practices, and that fairly represented the previously agreed upon terms in the executed letter of intent, with such changes as the parties had mutually agreed.

On September 30, 2022, Mr. Burgess, Mr. Cosby, other members of the First Bancshares management team, representatives of Stephens and representatives of Fenimore conducted a reverse due diligence conference call with senior management of Prosperity covering Prosperity’s corporate strategy, credit quality and loan portfolio trends, financial performance for 2021 and year-to-date 2022 and key assumptions related to Prosperity’s projected performance and earnings, certain operational matters and regulatory compliance and legal matters.

On October 7, 2022, the First Bancshares board of directors held a special meeting to analyze and further consider the negotiated terms of the proposed First Bancshares merger and entry into the First Bancshares reorganization agreement by First Bancshares. Members of First Bancshares’ management and representatives of Stephens and Fenimore also attended this meeting. Stephens reviewed its financial analysis of the proposed First Bancshares merger with the First Bancshares board of directors. Representatives of Fenimore provided a summary of the proposed terms of the First Bancshares reorganization agreement and the ancillary agreements and reviewed the First Bancshares board of directors’ fiduciary duties in connection with its evaluation of the potential merger. Following these discussions, and after further discussion of the proposed financial terms of the transaction and consideration of the strategic merits and potential risks and uncertainties for First Bancshares and its shareholders and other constituencies, the First Bancshares board of directors expressed support for the transaction and directed First Bancshares management and First Bancshares’ advisors to seek to finalize the terms of the potential transaction.

On October 10, 2022, the First Bancshares board of directors held a special meeting to consider the negotiated terms of the proposed merger between Prosperity and First Bancshares and the entry into the First Bancshares reorganization agreement by First Bancshares. At the meeting, members of First Bancshares management and representatives of Fenimore provided an update on the results of the negotiations since the October 7, 2022 board meeting, reviewed the proposed terms of the potential transaction and advised that the negotiations and definitive transaction documents were substantially complete. Stephens reviewed the financial aspects of the proposed First Bancshares merger and rendered its oral opinion, which was subsequently confirmed by delivery of a written opinion to the First Bancshares board of directors dated as of October 10, 2022, that, as of such date, the consideration to be received by the holders of First Bancshares common stock (solely in their capacity as such) in the proposed First Bancshares merger was fair to them from a financial point of view, based upon and subject to the qualifications, assumptions and other matters considered by Stephens in connection with the preparation of its opinion. Representatives of Fenimore described the resolutions the board of First Bancshares would be asked to consider if it was to approve the potential transaction. Thereafter, management of First Bancshares confirmed its recommendation of the proposed transaction to the First Bancshares board of directors. At the conclusion of the meeting, after further review and discussion by the First Bancshares board of directors, including consideration of the factors described under the section below entitled “ —First Bancshares’ Reasons for the First Bancshares Merger and Recommendation of the First Bancshares Board of Directors,” the First Bancshares board of directors determined that the First Bancshares reorganization agreement and the transactions contemplated thereby were advisable and in the best interests of First Bancshares and its shareholders, and unanimously approved the First Bancshares reorganization agreement and the transactions contemplated thereby and entry into the First Bancshares reorganization agreement by First Bancshares.

Prosperity and First Bancshares executed the First Bancshares reorganization agreement and related ancillary agreements discussed in this proxy statement/prospectus on October 10, 2022.

The First Bancshares merger was announced the morning of October 11, 2022, before the opening of the financial markets in New York, in a joint press release issued by Prosperity and First Bancshares.

First Bancshares’ Reasons for the First Bancshares Merger and Recommendation of the First Bancshares Board of Directors

The First Bancshares board of directors believes that the First Bancshares merger is in the best interests of First Bancshares and the First Bancshares shareholders. Accordingly, the First Bancshares board of directors has approved the First Bancshares reorganization agreement and unanimously recommends that the First Bancshares shareholders vote “FOR” approval of the First Bancshares merger proposal.

In reaching its decision to approve the First Bancshares reorganization agreement and to recommend its approval to First Bancshares shareholders, the First Bancshares board of directors evaluated the First Bancshares merger and the First Bancshares reorganization agreement in consultation with its executive management, Stephens, First Bancshares’ outside financial advisor, and First Bancshares’ legal counsel. In arriving at its recommendation, the First Bancshares board of directors considered a number of factors, including the following:

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the First Bancshares board of directors’ familiarity with and review of the information concerning the business, results of operations, financial condition, competitive position and future prospects of First Bancshares and FirstCapital Bank;

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the First Bancshares board of directors’ knowledge of the current environment in the financial services industry, including national, regional and regional economic conditions, increased regulatory burdens, evolving trends in technology, increasing competition, the current financial market and regulatory conditions and the likely effects of these factors on First Bancshares’ and Prosperity’s potential growth, development, productivity, profitability and strategic options;

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the belief of the First Bancshares board of directors that the value of the First Bancshares merger consideration to be received by First Bancshares’ shareholders pursuant to the First Bancshares reorganization agreement represents a fair price for the shares of First Bancshares common stock;

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the historical performance of Prosperity and its common stock, including historical cash dividends;

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the results that First Bancshares could expect to obtain if it continued to operate independently, and the likely benefits to shareholders of that course of action, as compared with the value of the First Bancshares merger consideration offered by Prosperity and First Bancshares’ belief that a merger with Prosperity would allow First Bancshares shareholders to participate in the future performance of a combined company that would have better future prospects than First Bancshares was likely to achieve on a stand-alone basis or through other strategic alternatives;

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the belief of the First Bancshares board of directors that Prosperity emphasizes many of the same values embraced by First Bancshares in the conduct of its business, such as excellent customer service, employee development and delivering value to shareholders;

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that a merger with a larger bank holding company could provide the opportunity to realize economies of scale, add infrastructure and operational support and enhance customer products and services;

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the likelihood of Prosperity successfully consummating the First Bancshares merger and integrating First Bancshares’ operations based on Prosperity’s history of merger transactions;

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the treatment of the First Bancshares merger as a “reorganization” within the meaning of Section 368(a) of the Code with the respect to the First Bancshares common stock exchanged for Prosperity common stock;

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the limited liquidity that First Bancshares shareholders have with respect to their investment in First Bancshares, for which there is no active public market, and that shareholders of First Bancshares will receive a portion of the First Bancshares merger consideration in shares of Prosperity common stock,

which is publicly traded on the NYSE, which would be expected to provide such shareholders with increased liquidity of their investment;

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the fact that the First Bancshares stock consideration would allow former First Bancshares shareholders to participate as Prosperity shareholders in the growth of Prosperity and in any synergies resulting from the First Bancshares merger;

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the immediate liquidity to First Bancshares shareholders as reflected by the First Bancshares cash consideration;

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the opinion rendered to the First Bancshares board of directors by Stephens to the effect that, as of October 10, 2022, and based on and subject to the various assumptions made, procedures followed, matters considered and limitations and qualifications on the review undertaken by Stephens as described in such written opinion, the consideration to be received by the holders of First Bancshares common stock (solely in their capacity as such) in the proposed First Bancshares merger was fair to them from a financial point of view;

•

the fact that First Bancshares may continue to pay regular quarterly cash dividends on First Bancshares common stock in accordance with past practices, subject to the terms of the First Bancshares reorganization agreement;

•

the anticipated likelihood of Prosperity to obtain the requisite regulatory approvals in a timely manner and without unacceptable conditions;

•

the potential effect of the First Bancshares merger on First Bancshares’ employees, including the prospects for continued employment and other benefits agreed to be provided by Prosperity to First Bancshares’ employees; and

•

the terms and conditions of the First Bancshares reorganization agreement, including the parties’ respective representations, warranties, covenants and other agreements and the conditions to closing.

The First Bancshares board of directors also considered the risks and potential negative factors outlined below, but concluded that the anticipated benefits of combining with Prosperity were likely to outweigh substantially these risks and factors. These risks included:

•

the lack of control of the First Bancshares board of directors and First Bancshares’ shareholders over future operations and strategy of the combined company as compared to remaining independent;

•

the challenges of combining the businesses, assets and workforces of two financial institutions;

•

the potential risk of diverting management focus and resources from other strategic opportunities and from operational matters while working to implement the First Bancshares merger;

•

the risks and costs to First Bancshares if the First Bancshares merger is not completed;

•

the requirement under the First Bancshares reorganization agreement that First Bancshares conduct its business in the ordinary course and the other restrictions on the conduct of First Bancshares’ business before completion of the First Bancshares merger, which could delay or prevent First Bancshares from undertaking business opportunities that may arise before completion of the First Bancshares merger;

•

the possibility that First Bancshares may not be able to deliver $204 million in adjusted equity at closing of the First Bancshares merger, which would result in a reduction of the First Bancshares merger consideration;

•

that the value of the First Bancshares stock consideration will fluctuate between the date of the First Bancshares reorganization agreement and the closing date and will not be known at the time the First Bancshares shareholders vote on the First Bancshares merger proposal, and that any reduction in the value of Prosperity common stock will not, in and of itself, permit First Bancshares to terminate the First Bancshares reorganization agreement;

•

that the value of the Prosperity common stock to be issued to First Bancshares’ shareholders in the First Bancshares merger is reliant on the successful operation of Prosperity in the future as opposed to selling First Bancshares entirely for cash, which would deliver all value to First Bancshares shareholders upon closing of such a sale;

•

the fact that gain on the disposition of First Bancshares common stock would generally be taxable to U.S. holders for U.S. federal income tax purposes to the extent of the cash received in the First Bancshares merger;

•

the potential for unintended delays in the regulatory approval process;

•

the fact that the First Bancshares reorganization agreement prohibits First Bancshares from soliciting acquisition proposals or, subject to certain exceptions, engaging in negotiations concerning or providing nonpublic information to any person relating to an acquisition proposal, and the fact that First Bancshares would be obligated to pay a termination fee following the termination of the First Bancshares reorganization agreement under certain circumstances;

•

the interests of certain of First Bancshares’ directors and executive officers in the First Bancshares merger that are different from, or in addition to, their interests as First Bancshares shareholders, which are further described below under “—Financial Interests of First Bancshares’ Directors and Executive Officers in the First Bancshares Merger” beginning on page 64;

•

the requirement that First Bancshares submit the First Bancshares reorganization agreement to its shareholders for approval even if the First Bancshares board of directors withdraws its recommendation to approve the First Bancshares reorganization agreement, unless the First Bancshares reorganization agreement is terminated;

•

the risk that the anticipated benefits of the First Bancshares merger, including the realization of synergies and cost savings, may not be realized or may take longer than expected to be realized; and

•

the possible effects of the pendency or completion of the transactions contemplated by the First Bancshares reorganization agreement, including any suit, action or proceeding initiated in respect of the First Bancshares merger.

The reasons set out above for the First Bancshares merger are not intended to be exhaustive but are believed to include material factors considered by the First Bancshares board of directors in approving the First Bancshares merger. In reaching its determination, the First Bancshares board of directors did not assign any relative or specific weights to different factors, and individual directors may have given different weights to different factors.

The First Bancshares board of directors conducted an overall analysis of the factors described above as a whole, including thorough discussions with, and questioning of, its executive management and outside financial and legal advisors. Based on the reasons stated, the First Bancshares board of directors believed that the First Bancshares merger was in the best interest of First Bancshares’ shareholders and approved the First Bancshares reorganization agreement and the First Bancshares merger.

The foregoing explanation of the First Bancshares board of directors’ reasoning and all other information presented in this section is forward-looking in nature and, therefore, should be read in light of the factors discussed in the section entitled “Cautionary Note Regarding Forward-Looking Statements” beginning on page 29.

Each of the directors and certain executive officers of First Bancshares, in their capacities as individuals, entered into First Bancshares voting agreements with Prosperity and First Bancshares pursuant to which they agreed to vote “FOR” the First Bancshares merger proposal and “FOR” any other matters required to be approved by the First Bancshares shareholders in furtherance of the First Bancshares merger proposal. For more information regarding the First Bancshares voting agreements, please see the section entitled “The Reorganization Agreements—Voting Agreements” beginning on page 107.

FIRST BANCSHARES’ BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT FIRST BANCSHARES SHAREHOLDERS VOTE “FOR” THE PROPOSAL TO APPROVE THE FIRST BANCSHARES REORGANIZATION AGREEMENT AND THE TRANSACTIONS CONTEMPLATED THEREBY.

Prosperity’s Reasons for the First Bancshares Merger

As a part of Prosperity’s growth strategy, Prosperity routinely evaluates opportunities to acquire financial institutions. The acquisition of First Bancshares is consistent with Prosperity’s expansion strategy. Prosperity’s board of directors, senior management and certain lenders reviewed the business, financial condition, results of operation and prospects for First Bancshares, the market condition of the market area in which First Bancshares conducts business, the compatibility of the management and the proposed financial terms of the First Bancshares merger. In addition, management of Prosperity believes that the First Bancshares merger will enhance Prosperity’s presence in the Wichita Falls and Amarillo markets and the Horseshoe Bay, Marble Falls and Fredericksburg markets in the high-growth Central Texas area, provide opportunities for future growth and provide the potential to realize cost savings. Prosperity’s board of directors also considered the financial condition and valuation for both First Bancshares and Prosperity as well as the financial and other effects the First Bancshares merger would have on Prosperity’s shareholders.

While management of Prosperity believes that revenue opportunities will be achieved and costs savings will be obtained following the First Bancshares merger, Prosperity has not quantified the amount of enhancements or projected the areas of operation in which such enhancements will occur.

In view of the variety of factors considered in connection with its evaluation of the First Bancshares merger, the Prosperity board did not find it useful to and did not attempt to quantify, rank or otherwise assign relative weights to factors it considered. Further, individual directors may have given differing weights to different factors. In addition, the Prosperity board did not undertake to make any specific determination as to whether any particular factor, or any aspect of any particular factor, was favorable or unfavorable to its ultimate determination. Rather, the Prosperity board conducted an overall analysis of the factors it considered material, including thorough discussions with, and questioning of, Prosperity’s management.

Opinion of First Bancshares’ Financial Advisor

On March 18, 2022, First Bancshares engaged Stephens to act as financial adviser to First Bancshares in connection with any proposed transaction involving First Bancshares and one or more parties. As part of its engagement, Stephens assisted First Bancshares in connection with the proposed merger of First Bancshares with and into Prosperity and was asked by First Bancshares to undertake a study of the fairness, from a financial point of view, of the consideration payable in connection with the proposed First Bancshares merger. First Bancshares engaged Stephens because, among other factors, Stephens is a nationally recognized investment banking firm with substantial experience in similar transactions. As part of its investment banking business, Stephens is continually engaged in the valuation of financial services businesses and their securities in connection with mergers and acquisitions.

As part of Stephens’ engagement, representatives of Stephens participated in a meeting of the First Bancshares board of directors held on October 10, 2022 in which the First Bancshares board of directors considered and approved the proposed First Bancshares merger. At this meeting, Stephens reviewed the financial aspects of the proposed First Bancshares merger and rendered its oral opinion, which was subsequently confirmed by delivery of a written opinion to the First Bancshares board of directors dated as of October 10, 2022, that, as of such date, the consideration to be received by the shareholders of First Bancshares (solely in their capacity as such) in the proposed First Bancshares merger was fair to them from a financial point of view, based upon and subject to the qualifications, assumptions and other matters considered by Stephens in connection with the preparation of its opinion.

The full text of Stephens’ written opinion letter, which we refer to as the “First Bancshares Opinion Letter,” is attached as Appendix G to this proxy statement/prospectus. The First Bancshares Opinion Letter outlines the procedures followed, assumptions made, matters considered and qualifications and limitations on the review undertaken by Stephens in rendering its opinion. The summary of the opinion set forth in this document is qualified in its entirety by reference to the full text of such written First Bancshares Opinion Letter. Investors are urged to read the entire First Bancshares Opinion Letter carefully in connection with their consideration of the proposed merger. First Bancshares did not give any instruction to or impose any limitations on Stephens as it related to the issuance of its opinion.

Stephens’ opinion speaks only as of the date of the opinion, and Stephens has undertaken no obligation to update or revise its opinion. The opinion was directed to the First Bancshares board of directors (solely in its capacity as such) in connection with, and for purposes of, its consideration of the proposed First Bancshares merger. The opinion only addresses whether the consideration to be received by the shareholders of First Bancshares (solely in their capacity as such) in the proposed First Bancshares merger was fair to them from a financial point of view as of the date of the opinion. The opinion does not address the underlying business decision of First Bancshares to engage in the proposed First Bancshares merger or any other term or aspect of the First Bancshares reorganization agreement or the transactions contemplated thereby. Stephens’ opinion does not constitute a recommendation to the First Bancshares board of directors or any of First Bancshares’ shareholders as to how such person should vote or otherwise act with respect to the proposed First Bancshares merger or any other matter. First Bancshares and Prosperity determined the First Bancshares merger consideration through a negotiation process.

In connection with developing its opinion, Stephens:

•

reviewed certain publicly available financial statements and reports regarding First Bancshares and Prosperity;

•

reviewed certain audited financial statements regarding First Bancshares and Prosperity;

•

reviewed certain internal financial statements, management reports and other financial and operating data concerning First Bancshares prepared by management of First Bancshares;

•

reviewed, on a pro forma basis, in reliance upon financial projections and other information and assumptions concerning First Bancshares provided by management of First Bancshares, and consensus research estimates regarding Prosperity, the effect of the proposed First Bancshares merger on the balance sheet, capitalization ratios, earnings and tangible book value both in the aggregate and, where applicable, on a per share basis of Prosperity;

•

reviewed the reported prices and trading activity for the common stock of Prosperity;

•

compared the financial performance of First Bancshares with that of certain other publicly traded companies and their securities that Stephens deemed relevant to Stephens’ analysis of the proposed First Bancshares merger;

•

reviewed the financial terms, to the extent publicly available, of certain merger or acquisition transactions that Stephens deemed relevant to Stephens’ analysis of the proposed First Bancshares merger;

•

reviewed the then most recent draft of the First Bancshares reorganization agreement and related documents provided to Stephens by First Bancshares;

•

discussed with management of First Bancshares and management of Prosperity the operations of and future business prospects for First Bancshares and Prosperity, respectively and the anticipated financial consequences of the proposed First Bancshares merger to First Bancshares and the Prosperity, respectively;

•

assisted in First Bancshares’ deliberations regarding the material terms of the proposed First Bancshares merger and First Bancshares’ negotiations with Prosperity; and

•

performed such other analyses and provided such other services as Stephens deemed appropriate.

Stephens relied on the accuracy and completeness of the information, financial data and financial forecasts provided to Stephens by First Bancshares and Prosperity and of the other information reviewed by Stephens in connection with the preparation of Stephens’ opinion, and its opinion was based upon such information. Stephens did not independently verify or undertake any responsibility to independently verify the accuracy or completeness of any of such information, data or forecasts. Management of First Bancshares assured Stephens that it was not aware of any relevant information that had been omitted or remained undisclosed to Stephens. Stephens did not assume any responsibility for making or undertaking an independent evaluation or appraisal of any of the assets or liabilities of First Bancshares or of Prosperity, and Stephens was not furnished with any such evaluations or appraisals; nor did Stephens evaluate the solvency or fair value of First Bancshares or of Prosperity under any laws relating to bankruptcy, insolvency or similar matters. Stephens did not assume any obligation to conduct any physical inspection of the properties, facilities, assets or liabilities (contingent or otherwise) of First Bancshares or Prosperity. Stephens did not receive or review any individual loan or credit files nor did Stephens make an independent evaluation of the adequacy of the allowance for loan and lease losses of First Bancshares or Prosperity. Stephens did not make an independent analysis of the effects of the COVID-19 pandemic, the invasion of Ukraine, potential future changes in the inflation rate or other related market developments or disruptions, or of any other disaster or adversity, on the business or prospects of First Bancshares or Prosperity. With respect to the financial forecasts prepared by management of First Bancshares and management of Prosperity, including the forecasts of potential cost savings and potential synergies, Stephens assumed that such financial forecasts had been reasonably prepared and reflected the best then currently available estimates and judgments of management of First Bancshares and management of Prosperity, respectively, as to the future financial performance of First Bancshares and Prosperity, respectively, and provided a reasonable basis for Stephens’ analysis. Stephens recognized that such financial forecasts were based on numerous variables, assumptions and judgments that were inherently uncertain (including, without limitation, factors related to general economic and competitive conditions) and that actual results could vary significantly from such forecasts, and Stephens expressed no opinion as to the reliability of such financial projections and estimates or the assumptions upon which they were based. For a discussion of the financial forecasts and other prospective financial information made available by First Bancshares to Stephens for the purpose of Stephens performing its financial analysis in connection with rendering its opinion to the First Bancshares board of directors, please see the section entitled “—Certain Unaudited Prospective Financial Information” beginning on page 62.

Stephens does not provide legal, accounting, regulatory, or tax advice or expertise, and Stephens relied solely, and without independent verification, on the assessments of First Bancshares and its other advisors with respect to such matters. Stephens assumed, with First Bancshares’ consent, that the proposed First Bancshares merger will not result in any materially adverse legal, regulatory, accounting or tax consequences for First Bancshares or its shareholders and that any reviews of legal, accounting, regulatory or tax issues conducted as a result of the proposed First Bancshares merger will be resolved favorably to First Bancshares and its shareholders. Stephens did not express any opinion as to any tax or other consequences that might result from the proposed First Bancshares merger.

Bancshares or Prosperity, and Stephens did not express an opinion as to the effects of such volatility or such disruption on the proposed First Bancshares merger or any party to the proposed First Bancshares merger. Stephens further expressed no opinion as to the prices at which shares of First Bancshares’ or Prosperity’s common stock may trade at any time subsequent to the announcement of the proposed First Bancshares merger.

In connection with developing its opinion, Stephens assumed that, in all respects material to its analyses:

•

the proposed First Bancshares merger and any related transactions will be consummated on the terms of the latest draft of the First Bancshares reorganization agreement provided to Stephens, without material waiver or modification;

•

the representations and warranties of each party in the First Bancshares reorganization agreement and in all related documents and instruments referred to in the First Bancshares reorganization agreement are true and correct;

•

each party to the First Bancshares reorganization agreement and all related documents will perform all of the covenants and agreements required to be performed by such party under such documents;

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all conditions to the completion of the proposed First Bancshares merger will be satisfied within the time frames contemplated by the First Bancshares reorganization agreement without any waivers;

•

that in the course of obtaining the necessary regulatory, lending or other consents or approvals (contractual or otherwise) for the proposed First Bancshares merger and any related transactions, no restrictions, including any divestiture requirements or amendments or modifications, will be imposed that would have a material adverse effect on the contemplated benefits of the proposed First Bancshares merger to the shareholders of First Bancshares;

•

there has been no material change in the assets, liabilities, financial condition, results of operations, business or prospects of First Bancshares or Prosperity since the date of the most recent financial statements made available to Stephens, and that no legal, political, economic, regulatory or other development has occurred that will adversely impact First Bancshares or Prosperity; and

•

the proposed First Bancshares merger will be consummated in a manner that complies with applicable law and regulations.

Stephens’ opinion was limited to whether the consideration to be received by the shareholders of First Bancshares (solely in their capacity as such) in the proposed First Bancshares merger was fair to them from a financial point of view as of the date of the opinion. Stephens was not asked to, and it did not, offer any opinion as to the terms of the First Bancshares reorganization agreement or the form of the proposed First Bancshares merger or any aspect of the proposed First Bancshares merger, other than the fairness, from a financial point of view, of the consideration to be received in the proposed First Bancshares merger by the shareholders of First Bancshares (solely in their capacity as such). The opinion did not address the merits of the underlying decision by First Bancshares to engage in the proposed First Bancshares merger, the merits of the proposed First Bancshares merger as compared to other alternatives potentially available to First Bancshares or the relative effects of any alternative transaction in which First Bancshares might engage, nor is it intended to be a recommendation to any person or entity as to any specific action that should be taken in connection with the proposed First Bancshares merger, including with respect to how to vote or act with respect to the proposed First Bancshares merger. Moreover, Stephens did not express any opinion as to the fairness of the amount or nature of the compensation to any of First Bancshares’ officers, directors or employees, or to any group of such officers, directors or employees, whether relative to the compensation to other shareholders of First Bancshares or otherwise.

directors the assumptions upon which the analyses were based, as well as other factors. Although this summary does not purport to describe all of the analyses performed or factors considered by Stephens, it does set forth those analyses considered by Stephens to be material in arriving at its opinion. The preparation of a fairness opinion is a complex analytic process involving various determinations as to the appropriate and relevant methods of financial analysis and the application of those methods to the particular circumstances. Therefore, a fairness opinion is not readily susceptible to partial analysis or summary description. The order of the summaries of analyses described does not represent the relative importance or weight given to those analyses by Stephens. It should be noted that in arriving at its opinion, Stephens did not attribute any particular weight to any analysis or factor considered by it, but rather made qualitative judgments as to the significance and relevance of each analysis and factor. Accordingly, Stephens believes that its analysis must be considered as a whole and that considering any portion of such analyses and factors, without considering all analyses and factors as a whole, could create a misleading or incomplete view of the process underlying its opinion. The financial analyses summarized below include information presented in tabular format. The tables alone do not constitute a complete description of the financial analyses summarized below. Accordingly, Stephens’ analyses and the summary of its analyses must be considered as a whole, and selecting portions of its analyses and factors or focusing on the information presented below in tabular format, without considering all analyses and factors or the full narrative description of the financial analyses, including the methodologies and assumptions underlying the analyses, could create a misleading or incomplete view of the process underlying Stephens’ analyses and opinion.

Summary of Proposed First Bancshares Merger

Pursuant to the First Bancshares reorganization agreement, and subject to the terms, conditions and limitations set forth therein, and for purposes of its opinion, Stephens understood that, subject to potential adjustments as described in the First Bancshares reorganization agreement, the consideration expected to be exchanged by Prosperity for all of the outstanding common stock and options on the common stock of First Bancshares has an aggregate value of approximately $350.4 million and will consist of 3,583,370 shares of Prosperity’s common stock and $93,422,648 in cash. Stephens further understood that under the First Bancshares reorganization agreement each share of First Bancshares’ outstanding common stock will be entitled to receive approximately 0.2119 shares of Prosperity’s common stock and approximately $5.32 in cash, which is based on Prosperity’s closing stock price of $71.71 on October 4, 2022. Based upon the unaudited financial information of First Bancshares as of and for the twelve months ended June 30, 2022 and market data as of October 4, 2022 Stephens calculated the following transaction multiples:


Transaction Value / Reported Tangible Book Value	1.67x
Transaction Value / Adjusted Tangible Book Value (9.0%)	1.76x
Transaction Value / Last Twelve Months Earnings	12.5x
Core Deposit Premium	9.4	%

Note: The last twelve months earnings of First Bancshares is based on the most recent available financial statements prior to announcement of the First Bancshares merger.

Relevant Public Companies Analysis

Stephens compared the financial condition, operating statistics and market valuation of First Bancshares to certain public companies selected by Stephens and their respective public trading values. Stephens selected the companies outlined below because their relative asset size and financial performance, among other factors, were reasonably similar to First Bancshares; however, no selected company below was identical or directly comparable to First Bancshares. A complete analysis involves complex considerations and qualitative judgments concerning differences in financial and operating characteristics and other factors that could affect the public trading values of the relevant public companies. Mathematical analysis (such as determining the median) is not in itself a meaningful method of using relevant public company data.

Stephens selected the following public companies based on the criteria set forth below:

Nationwide major exchange traded banks between $1.5 billion and $3.0 billion in total assets, a last twelve months return on average assets greater than 1.20%, and a loans to deposits ratio less than 100%.


• Bank First Corporation		• USCB Financial Holdings, Inc.

• Five Star Bancorp		• Parke Bancorp, Inc.

• Blue Ridge Bankshares, Inc.		• OP Bancorp

• The First Bancorp, Inc.		• Meridian Corporation

• Citizens & Northern Corporation		• MainStreet Bancshares, Inc.

• PCB Bancorp		• Hawthorn Bancshares, Inc.

• John Marshall Bancorp, Inc.		• First United Corporation

• Citizens Financial Services, Inc.		• National Bankshares, Inc.

• Capital Bancorp, Inc.		• FNCB Bancorp, Inc.

• Norwood Financial Corp.		• Plumas Bancorp

To perform this analysis, Stephens reviewed publicly available financial information as of and for the last twelve-month period ended June 30, 2022 or the most recently reported period available, and the market trading multiples of the selected public companies based on October 4, 2022 closing prices. The financial data included in the table presented below may not correspond precisely to the data reported in historical financial statements as a result of the assumptions and methods used by Stephens to compute the financial data presented. The table below contains information reviewed and utilized by Stephens in its analysis:


	First Bancshares			25^th Percentile			Median			75^th Percentile
Total Assets (in billions)	$	2.1		$	1.8		$	2.0		$	2.4
Tangible Common Equity / Total Assets		10.2	%		7.5	%		8.2	%		8.8	%
Price / Tangible Book Value		1.67x			1.10x			1.50x			1.67x
Price / Adj. Tangible Book Value (9.0%)		1.76x			1.08x			1.41x			1.62x
Price / Last Twelve Months Net Income		12.5x			6.8x			8.1x			9.6x

Source: S&P Capital IQ Pro and FactSet.

Discounted Cash Flow Analysis

Stephens performed a standalone discounted cash flow analysis using projections developed by the executive management team of First Bancshares and then calculated a range of implied equity values for First Bancshares based upon the discounted net present value of the projected after-tax free cash flows for the projected period. Stephens determined the amount of cash flow assuming (i) a terminal earnings multiple of 9.0x, (ii) dividend payments for earnings and excess capital above a tangible common equity to tangible asset ratio of 9.0% from 2022 to 2026 and (iii) the present value of First Bancshares’ implied standalone terminal values at the end of such period. Stephens calculated the terminal values of First Bancshares based on 2027 estimated earnings and multiples of 8.0x to 10.0x. Stephens considered discount rates from 8.5% to 10.5% for First Bancshares. Based on this analysis, Stephens derived a range for the implied equity value of First Bancshares from $21.52 per share to $26.72 per share.

values or expected values of First Bancshares. The actual results may vary from the projected results, any of these assumptions might not be realized in future operations and the variations may be material. For a discussion of the financial forecasts and other prospective financial information made available by First Bancshares to Stephens for the purpose of Stephens performing its financial analysis in connection with rendering its opinion to the First Bancshares board of directors, please see the section entitled “—Certain Unaudited Prospective Financial Information” beginning on page 62.

Relevant Nationwide Transactions Analysis

Stephens reviewed certain publicly available transaction multiples and related financial data for transactions nationwide announced since 2020, where (i) the deal value was publicly disclosed, (ii) the target’s assets were between $1.5 billion and $3.0 billion, (iii) the target’s last twelve months return on average assets was greater than 1.00% and (iv) the target’s tangible common equity to tangible assets ratio was greater than 8.00% (excluding any Merger of Equals (as defined by S&P Global Market Intelligence)). The following transactions were selected by Stephens because each target’s relative asset size, financial performance and operations, among other factors, was reasonably similar to First Bancshares; however, no selected company or transaction below was identical or directly comparable to First Bancshares or the proposed First Bancshares merger (in each transaction, the acquirer is listed first and the target is listed second):

•

United Community Banks, Inc./Progress Financial Corporation

•

Origin Bancorp, Inc./BT Holdings, Inc.

•

Lakeland Bancorp, Inc./1st Constitution Bancorp

•

Columbia Banking System, Inc./Bank of Commerce Holdings

•

United Bankshares, Inc./Community Bankers Trust Corporation

•

Enterprise Financial Services Corp/First Choice Bancorp

•

Peoples Bancorp Inc./Premier Financial Bancorp, Inc.

•

Provident Financial Services, Inc./SB One Bancorp

Stephens considered these selected transactions to be reasonably similar, but not identical or directly comparable, to the proposed First Bancshares merger. A complete analysis involves complex considerations and qualitative judgments concerning differences in the selected transactions and other factors that could affect the transaction values in those selected transactions as compared with the proposed First Bancshares merger. Mathematical analysis (such as determining the median) is not in itself a meaningful method of using selected transaction data. Stephens compared certain proposed transaction multiples of the proposed First Bancshares merger to the 25^th percentile, median and 75^th percentile transaction multiples of the selected transactions:


	First Bancshares			25^th Percentile			Median			75^th Percentile
Deal Value (in millions)	$	350		$	262		$	281		$	307
Target Total Assets (in billions)	$	2.1		$	1.8		$	1.9		$	2.0
Target Tangible Common Equity / Total Assets		10.2	%		8.8	%		9.0	%		10.5	%
Target Last Twelve Months Return on Average Assets		1.35	%		1.18	%		1.20	%		1.28	%
Transaction Value / Tangible Book Value		1.67x			1.49x			1.60x			1.66x
Transaction Value / Adj. Tangible Book Value (9.0%)		1.76x			1.52x			1.64x			1.69x
Transaction Value / Last Twelve Months Earnings		12.5x			11.5x			13.1x			13.9x
Core Deposit Premium		9.4	%		6.5	%		7.9	%		9.3	%

Source: S&P Capital IQ Pro, First Bancshares management and draft First Bancshares reorganization agreement.

Relevant Texas Transactions Analysis

Stephens reviewed certain publicly available transaction multiples and related financial data for transactions with a target headquarters domiciled in Texas announced since 2020, where (i) the deal value was publicly disclosed, and (ii) the target’s assets were between $500 million and $10 billion (excluding any Merger of Equals (as defined by S&P Global Market Intelligence)). The following transactions were selected by Stephens because each target’s relative asset size, financial performance and markets of operation, among other factors, was reasonably similar to First Bancshares; however, no selected company or transaction below was identical or directly comparable to First Bancshares or the proposed First Bancshares merger (in each transaction, the acquirer is listed first and the target is listed second):

•

Origin Bancorp, Inc./BT Holdings, Inc.

•

Simmons First National Corporation/Spirit of Texas Bancshares, Inc.

•

Business First Bancshares, Inc./Texas Citizens Bancorp, Inc.

•

Home Bancshares, Inc./Happy Bancshares, Inc.

•

BancorpSouth Bank/National United Bancshares, Inc.

•

Heartland Financial USA, Inc./AIM Bancshares, Inc.


	First Bancshares			25^th Percentile			Median			75^th Percentile
Deal Value (in millions)	$	350		$	156		$	297		$	515
Target Total Assets (in billions)	$	2.1		$	1.0		$	1.9		$	2.9
Target Tangible Common Equity / Total Assets		10.2	%		8.1	%		9.5	%		10.2	%
Target Last Twelve Months Return on Average Assets		1.35	%		1.15	%		1.28	%		1.39	%
Transaction Value / Tangible Book Value		1.67x			1.56x			1.58x			1.77x
Transaction Value / Adj. Tangible Book Value (9.0%)		1.76x			1.60x			1.63x			1.87x
Transaction Value / Last Twelve Months Earnings		12.5x			12.7x			13.6x			15.3x
Core Deposit Premium		9.4	%		6.9	%		7.6	%		11.2	%

Source: S&P Capital IQ Pro, First Bancshares management and draft First Bancshares reorganization agreement.

Miscellaneous

The preparation of a fairness opinion is a complex process and is not susceptible to a partial analysis or summary description. Stephens believes that its analyses must be considered as a whole and that selecting portions of its analyses, without considering the analyses taken as a whole, would create an incomplete view of the process underlying its opinion. In addition, Stephens considered the results of all such analyses and did not assign relative weights to any of the analyses, but rather made qualitative judgments as to significance and

relevance of each analysis and factor, so the results from any particular analysis described above should not be taken to be the view of Stephens.

In performing its analyses, Stephens made numerous assumptions with respect to industry performance, general business, economic and regulatory conditions and other matters, many of which are beyond the control of First Bancshares. The analyses performed by Stephens are not necessarily indicative of actual values, trading values or actual future results which might be achieved, all of which may be significantly more or less favorable than suggested by such analyses. The analyses do not purport to be appraisals or to reflect the prices at which companies may actually be sold, and such estimates are inherently subject to uncertainty.

Stephens is serving as financial adviser to First Bancshares in connection with the proposed First Bancshares merger and is entitled to receive from First Bancshares reimbursement of its expenses and a fee for its services as financial advisor to First Bancshares, a significant portion of which is contingent upon the consummation of the proposed First Bancshares merger. Stephens also received a fee from First Bancshares upon rendering its fairness opinion, which opinion fee will be credited in full against the fee which will become payable to Stephens upon the closing of the proposed First Bancshares merger. First Bancshares has also agreed to indemnify Stephens against certain claims and liabilities that could arise out of Stephens’ engagement, including certain liabilities that could arise out of Stephens’ providing its opinion.

Stephens issues periodic research reports regarding the business and prospects of Prosperity, and Stephens makes a market in the stock of Prosperity. Stephens has not received fees for providing investment banking services to First Bancshares or Prosperity within the past two years. Stephens expects to pursue future investment banking services assignments with participants in the proposed First Bancshares merger transaction.

In the ordinary course of its business, Stephens Inc. and its affiliates and employees at any time may hold long or short positions, and may trade or otherwise effect transactions as principal or for the accounts of customers, in debt, equity or derivative securities of participants in the proposed First Bancshares merger.

Certain Unaudited Prospective Financial Information

Prosperity and First Bancshares do not as a matter of course make public projections as to future performance, revenues, earnings or other financial results due to, among other reasons, the inherent uncertainty of the underlying assumptions and estimates of any such projections. However, First Bancshares is including in this proxy statement/prospectus certain unaudited prospective financial information that was made available by First Bancshares to Stephens for the purpose of Stephens performing its financial analysis in connection with rendering its opinion to the First Bancshares board of directors, as described above under the section entitled “—Opinion of First Bancshares’ Financial Advisor.” This unaudited prospective financial information was prepared solely by First Bancshares management and was not prepared, provided to, reviewed or approved by Prosperity management or the Prosperity board of directors. By inclusion of this information, the respective managements and boards of directors of Prosperity and First Bancshares and First Bancshares’ financial advisor, assume no responsibility for the unaudited prospective financial information. The inclusion of this information should not be regarded as an indication that any of Prosperity, First Bancshares, Stephens, their respective representatives or any other recipient of this information considered, or now considers, it to be necessarily predictive of actual future results, or that it should be construed as financial guidance, and it should not be relied on as such.

The information regarding First Bancshares below was prepared solely by First Bancshares management for internal use and is subjective in many respects. While presented with numeric specificity, the unaudited prospective financial information reflects numerous estimates and assumptions made solely by First Bancshares management with respect to business, economic, market, competition, regulatory and financial conditions and matters specific to First Bancshares’ business, all of which are difficult to predict and many of which are beyond First Bancshares’ control. The unaudited prospective financial information of First Bancshares reflects both

assumptions solely by First Bancshares management as to certain business decisions that are subject to change and, in many respects, subjective judgment solely by First Bancshares management, and thus is susceptible to multiple interpretations and periodic revisions based on actual experience and business developments. No assurance can be given that the unaudited prospective financial information and the underlying estimates and assumptions will be realized. Actual results may differ materially from those set forth below, and important factors that may affect actual results and cause the unaudited prospective financial information to be inaccurate include, but are not limited to, risks and uncertainties relating to First Bancshares’ business, industry performance, general business and economic conditions, competition, customer requirements and adverse changes in applicable laws, regulations or rules. For other factors that could cause actual results to differ, see the sections entitled “Risk Factors” beginning on page 33 and “Cautionary Note Regarding Forward-Looking Statements” beginning on page 29.

The unaudited prospective financial information was not prepared by First Bancshares management with a view toward public disclosure, nor was it prepared with a view toward compliance with GAAP, the prevailing practices in the banking industry, published guidelines of the SEC or the guidelines established by the American Institute of Certified Public Accountants for preparation and presentation of prospective financial information. In addition, the unaudited prospective financial information requires significant estimates and assumptions that make it inherently less comparable to the similarly titled GAAP measures in Prosperity’s and First Bancshares’ respective historical GAAP financial statements. Neither Prosperity’s nor First Bancshares’ independent public accountants nor any other independent accountants, have compiled, examined or performed any procedures with respect to the unaudited prospective financial information contained herein, nor have they expressed any opinion or any other form of assurance on such information or its achievability.

Furthermore, the unaudited prospective financial information does not take into account any circumstances or events occurring after the date it was prepared. No assurance can be given that, had the unaudited prospective financial information been prepared as of the date of this proxy statement/prospectus, similar estimates and assumptions would be used. Neither Prosperity nor First Bancshares intends to, and expressly disclaims any obligation to, make publicly available any update or other revision to the unaudited prospective financial information to reflect circumstances existing since their preparation or to reflect the occurrence of unanticipated events, even in the event that any or all of the underlying assumptions are shown to be in error, or to reflect changes in general economic or industry conditions. The unaudited prospective financial information does not take into account the possible financial and other effects of the First Bancshares merger and does not attempt to predict or suggest future results of the surviving company. The unaudited prospective financial information of First Bancshares is presented strictly on a stand-alone basis and does not give effect to the First Bancshares merger, including the impact of negotiating or executing the First Bancshares reorganization agreement, the expenses that may be incurred in connection with consummating the First Bancshares merger, the potential synergies that may be achieved by the surviving company as a result of the First Bancshares merger, the effect on First Bancshares of any business or strategic decision or action that has been or will be taken as a result of the First Bancshares reorganization agreement having been executed, or the effect of any business or strategic decisions or actions that would likely have been taken if the First Bancshares reorganization agreement had not been executed, but which were instead altered, accelerated, postponed or not taken in anticipation of the First Bancshares merger. Further, the unaudited prospective financial information does not take into account the effect on First Bancshares of any possible failure of the First Bancshares merger to occur.

None of Prosperity, First Bancshares, Stephens, or their respective affiliates, officers, directors, advisors or other representatives has made, makes or is authorized in the future to make any representation to any shareholder of Prosperity or First Bancshares or other persons regarding First Bancshares’ ultimate performance compared to the information contained in the unaudited prospective financial information or that the projected results will be achieved. The summary of the unaudited prospective financial information included below is not being included to influence your decision whether to vote for the First Bancshares merger proposal, but is being provided solely because it was made available to Stephens in connection with the First Bancshares merger.

In light of the foregoing, and considering that the First Bancshares special meeting will be held many months after the unaudited prospective financial information was prepared, as well as the uncertainties inherent in any forecasted information, First Bancshares shareholders are cautioned not to place unwarranted reliance on such information, and all First Bancshares shareholders are urged to review the other information contained elsewhere in this proxy statement/prospectus for a description of Prosperity’s and First Bancshares’ respective businesses, as well as Prosperity’s most recent SEC filings for a description of its reported financial results. See the section entitled “Where You Can Find More Information” beginning on page 141.

The following table presents selected unaudited prospective financial data of First Bancshares on a stand-alone basis and were prepared solely by First Bancshares management and approved by the First Bancshares board of directors for Stephens’ financial analysis in connection with rendering its opinion to the First Bancshares board of directors, as described in this proxy statement/prospectus under the section entitled “—Opinion of First Bancshares’ Financial Advisor.”


	As of or For the Years Ended December 31,
	2022		2023		2024		2025		2026
First Bancshares Net Income (in millions)	$	35.0	$	37.9	$	42.6	$	45.2	$	47.9
First Bancshares Total Assets (in billions)		2.2		2.3		2.5		2.6		2.8


	Assumed Long-Term Growth Rates for First Bancshares
Earnings (%)		6.0	%
Total Assets (%)		6.0	%

Financial Interests of First Bancshares’ Directors and Executive Officers in the First Bancshares Merger

In considering the recommendation of the First Bancshares board of directors that First Bancshares shareholders vote “FOR” the First Bancshares merger proposal, First Bancshares shareholders should be aware that some of First Bancshares’ executive officers and directors have interests in the First Bancshares merger, which may be considered to be different from, or in addition to, the interests of the First Bancshares shareholders generally. These interests are described below. The First Bancshares board of directors was aware of these interests and considered them, among other matters, in reaching its decision to approve the First Bancshares reorganization agreement, the First Bancshares merger and the other transactions contemplated by the First Bancshares reorganization agreement and to recommend that First Bancshares shareholders vote “FOR” the First Bancshares merger proposal.

Employment Agreements with Prosperity

As a material inducement to Prosperity to enter into the First Bancshares reorganization agreement, Prosperity Bank entered into employment agreements with certain of the executive officers of First Bancshares and FirstCapital Bank, which are designed to govern the terms and conditions of each such individual’s service relationship with Prosperity Bank following the effective time of the First Bancshares merger. Each agreement is for an initial term of three years, entitles the named individual to receive a base annual salary over the term of the agreement, sets forth the eligibility terms for bonuses and provides for participation in certain employee benefit plans and stock based compensation programs of Prosperity, among other things. Each agreement also sets forth the conditions under which the agreement may be terminated and contains non-competition and non-solicitation obligations for a specified period of time.

Deferred Cash Incentive Agreements

Prosperity’s obligation to complete the First Bancshares merger is subject to First Bancshares terminating and fully liquidating its deferred cash incentive agreements with certain officers. Under the terms of the First

Bancshares deferred cash incentive agreements, First Bancshares may provide deferred compensation to these officers as a percentage of the officer’s base salary based on certain performance-based criteria. Accrued amounts earn interest at fifty percent of FirstCapital Bank’s annual after-tax return on equity. Deferred cash incentive distributions are paid on an annual basis on December 31, beginning after the fourth anniversary of initial plan contributions. Upon the termination of the deferred cash incentive agreements immediately prior to the First Bancshares merger, First Bancshares must pay all accrued benefits to the officers that are parties to such agreements in a lump sum within sixty days of the termination. The aggregate amount of the accrued benefits that are expected to be paid to officers of First Bancshares prior to completion of the First Bancshares merger is approximately $1.5 million.

Change in Control Payments

FirstCapital Bank is a party to change in control agreements with certain of its officers, which provide, among other things, for change in control payments to be made in connection with the completion of the First Bancshares merger. Under the terms of the First Bancshares reorganization agreement, the after-tax amount of the change in control payments must be paid or properly accrued for by First Bancshares for purposes of calculating its adjusted tangible equity. The aggregate amount of the change in control payments that are expected to be paid to such individuals as a result of the completion of the First Bancshares merger is approximately $4.8 million.

Acceleration of Equity Awards

At the First Bancshares effective time, subject to the terms and conditions of the First Bancshares reorganization agreement, each option granted by First Bancshares to purchase shares of First Bancshares common stock under the First Bancshares equity compensation plans will fully vest and be cancelled and converted into the right to receive a cash payment equal to the difference between the per award share merger consideration (as defined in the First Bancshares reorganization agreement) and the per share exercise price for each share of First Bancshares common stock subject to such First Bancshares stock option. The following table sets forth holdings of First Bancshares stock options by its executive officers as of the First Bancshares record date:


Name of Optionholder	Number of Vested Options		Number of Non-Vested Options
Tracy Bacon		39,900		4,100
Phyllis Bechner		25,800		4,700
Jeremy Bishop		6,000		14,000
Brad D. Burgess		85,000		12,500
J. Greg Burgess		22,600		6,200
Ken L. Burgess, Jr.		152,000		20,500
Michael J. Canon		9,000		1,500
Don E. Cosby		115,000		10,000
Tommy L. McCulloch, Jr.		3,000		2,000
Robin Richey		3,000		7,000

Indemnification

The First Bancshares reorganization agreement provides that Prosperity will indemnify each director and officer of First Bancshares or FirstCapital Bank as of the effective time of the First Bancshares merger for a period of four years thereafter, against any costs or expenses (including reasonable attorneys’ fees), judgments, fines, losses, claims, damages or liabilities incurred in connection with any claim, action, suit, proceeding or investigation, whether civil, criminal, administrative or investigative, arising out of matters existing or occurring at or before the effective time of the merger, whether asserted or claimed before, at or after the effective time of

the First Bancshares merger, arising in whole or in part out of or pertaining to the fact that he or she was acting in his or her capacity as a director or officer of First Bancshares or FirstCapital Bank to the fullest extent that the indemnified party would be entitled under First Bancshares’ certificate of formation or bylaws or the similar constituent documents of FirstCapital Bank, as applicable, as in effect on the date of the reorganization agreement and to the extent permitted by applicable law.

THE LONE STAR MERGER

The following discussion contains material information regarding the Lone Star merger. The discussion is subject to, and qualified in its entirety by reference to, the Lone Star reorganization agreement, which is attached to this proxy statement/prospectus as Appendix B and is incorporated by reference into this proxy statement/prospectus. The following is not intended to provide factual information about the parties or any of their respective subsidiaries or affiliates. This discussion does not purport to be complete and may not contain all of the information about the Lone Star merger that is important to you. We urge you to read the Lone Star reorganization agreement carefully and in its entirety, as it is the legal document governing the Lone Star merger.

Terms of the Lone Star Merger

Prosperity and Lone Star are proposing a transaction in which Prosperity will acquire Lone Star by means of the merger of Lone Star with and into Prosperity, with Prosperity as the surviving corporation, and Lone Star Bank will merge with and into Prosperity Bank, with Prosperity Bank as the surviving bank. The Lone Star merger transaction is governed by the Lone Star reorganization agreement, which has been unanimously approved by both the Prosperity board of directors and the Lone Star board of directors.

If the Lone Star merger is completed, all shares of Lone Star common stock issued and outstanding immediately prior to the Lone Star effective time will be converted into an aggregate of 2,376,182 shares of Prosperity common stock and $64,053,717 in cash, less any amounts paid at closing with respect to outstanding equity awards, as set forth in the Lone Star reorganization agreement. Additionally, the aggregate Lone Star cash consideration will be reduced on a dollar-for-dollar basis if Lone Star’s equity capital, as calculated under the Lone Star reorganization agreement, is less than $121,088,508 at closing of the Lone Star merger. Because of the possibility of an adjustment to the Lone Star cash consideration, you will not know the exact amount of cash you will receive in connection with the Lone Star merger when you vote on the Lone Star reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each Lone Star shareholder will receive.

Lone Star shareholders are being asked to approve the Lone Star reorganization agreement, including the Lone Star merger and all transactions contemplated thereby. See the section entitled “The Reorganization Agreements” beginning on page 89 for additional and more detailed information regarding the legal documents that govern the Lone Star merger, including information about the conditions to consummation of the Lone Star merger and the provisions for terminating or amending the Lone Star reorganization agreement.

Background of the Lone Star Merger

As part of the ongoing consideration and evaluation of its long-term prospects and strategies, Lone Star’s board of directors and senior management have regularly reviewed and assessed their business strategies and objectives, including assessments of strategic growth opportunities potentially available to Lone Star. These strategic discussions have focused on, among other things, prospects and developments in the financial services industry, the regulatory environment, the economy and the financial markets generally, and the implications of such developments both for financial institutions generally and for Lone Star, in particular. These strategic discussions were part of the continuous efforts of Lone Star to enhance value for their respective shareholders and deliver the best possible services to its customers and communities. This strategic review has also included assessment of ongoing consolidation in the financial services industry and the benefits and risks to Lone Star and its shareholders of strategic combinations compared to the benefits and risks of continued operation as a stand-alone company. Factors assessed in connection with this review have included the benefits and risks of operating in existing and new markets, competition, potential expense and revenue synergies, regulatory requirements, the interest rate environment, scale and diversification, credit risk, market risk and the impacts of rapidly changing technology and the delivery channels for products and services.

The Lone Star board of directors initially determined to explore the possibility of a strategic combination transaction and engaged Stephens as financial advisor in early 2020. During the first quarter of 2020, Stephens solicited interest from five different potential partners, including Prosperity. However, as a result of the COVID-19 pandemic, the Lone Star board of directors suspended the process shortly thereafter.

In the summer of 2021, Stephens renewed discussions around a potential strategic transaction and Lone Star determined to resume the marketing process on a limited basis in order to be in a better position when the pandemic and the uncertainty surrounding it eventually subsided. During the second half of 2021 and first half of 2022, Stephens and Lone Star had discussions with seven potential partners, including Prosperity, in order to gauge their interest in a potential combination.

On June 29, 2022, representatives of Stephens met with members of Prosperity’s management team in Dallas, Texas, to discuss a potential transaction with Lone Star. As a result of Prosperity’s expressed interest in Lone Star, members of Prosperity and Lone Star’s respective management teams met, together with representatives of Stephens, in Lubbock, Texas, on July 12, 2022 to discuss a potential transaction. Thereafter, on July 18, 2022, the parties entered into a Non-Disclosure and Confidentiality Agreement to enable them to begin sharing information and further discussing a potential transaction.

On July 22, 2022, Prosperity provided Lone Star with a non-binding letter of intent that contemplated Prosperity acquiring all of the issued and outstanding shares of Lone Star common stock, and all outstanding equity-based awards, in exchange for 2,376,182 shares of Prosperity common stock and $64.1 million in cash consideration, subject to, among other things, completion of due diligence and entry into a definitive agreement. The proposed transaction was not subject to a financing contingency.

During the following week, members of Lone Star’s management and Stephens, in consultation with Lone Star’s outside legal counsel, Fenimore Kay Harrison LLP, or “Fenimore,” discussed and negotiated the terms of the letter of intent with Prosperity. On July 29, 2022, Prosperity provided a revised letter of intent to Lone Star, which contemplated the same transaction structure and purchase price, but made certain changes, including with respect to the provisions governing purchase price adjustments.

Following additional discussions between management of Lone Star and Lone Star’s advisors, the Lone Star board of directors met on August 1, 2022 to consider the non-binding letter of intent. At that meeting, representatives of Stephens presented to the Lone Star board of directors an evaluation of the financial terms of the Prosperity letter of intent in relation to relevant financial pricing metrics, discussed with the board the market for mergers and acquisitions, and led a discussion regarding various strategic alternatives that may be available to

Lone Star. As part of those discussions, the Lone Star board of directors discussed with representatives of Stephens an overview of Prosperity’s financial performance and expectations for a proposed transaction with Prosperity. The Lone Star board of directors also discussed the terms of the revised letter of intent. Following lengthy deliberations, the Lone Star board of directors voted unanimously to authorize management to enter into the non-binding letter of intent.

Following the execution of the non-binding letter of intent, the parties continued to engage in reciprocal due diligence and discussions on matters that would form the basis of a definitive agreement. Over this time, Lone Star provided Prosperity with access through an electronic data room with to various corporate, financial, legal, operational and compliance-related documents and responded to other specific information requests.

On September 12, 2022, legal counsel for Prosperity distributed a draft definitive agreement to Lone Star and its advisors, which formed the basis for the further negotiation of deal terms. Following the receipt of the draft definitive agreement, the parties continued to conduct and discuss the results of reciprocal due diligence, which included a joint management due diligence call on September 30, 2022 with representatives of both parties and their respective advisors. During this period, management of Lone Star and Prosperity also engaged in negotiations over the other business and legal terms of the proposed merger. Primary subjects of these negotiations included the scope of any purchase price adjustments, the manner of disposition of Lone Star equity-based awards, the scope of operational covenants, the scope of each party’s representations and warranties, employee matters, the scope of termination rights and the amounts of any fees and expense reimbursements upon certain termination events, regulatory matters and the scope of ancillary agreements. In addition, Prosperity provided drafts of employment agreements to certain identified employees of Lone Star relating to the terms of employment with Prosperity upon completion of the Lone Star merger.

On October 7, 2022, the Lone Star board of directors held a special meeting to analyze and further consider the negotiated terms of the Lone Star reorganization agreement and the Lone Star merger. Members of Lone Star management and representatives of Stephens and Fenimore also attended this meeting. Stephens reviewed its financial analysis of the proposed merger with the Lone Star board of directors and rendered to the Lone Star board of directors an oral opinion, which was subsequently confirmed by delivery of a written opinion, to the Lone Star board of directors to the effect that, as of the date of such written opinion and based on and subject to the various assumptions made, procedures followed, matters considered and limitations and qualifications on the review undertaken as described in such written opinion, the per share merger consideration set forth in the Lone Star reorganization agreement was fair, from a financial point of view, to holders of Lone Star common stock. Representatives of Fenimore then provided an updated summary of the proposed terms of the Lone Star reorganization agreement and the ancillary agreements, reviewed the Lone Star board of directors’ fiduciary duties in connection with its evaluation of the potential merger and described the resolutions the directors of Lone Star would be asked to consider if they were to approve the Lone Star merger. At the conclusion of the meeting, after careful review and deliberation by the Lone Star board of directors, including consideration of the factors described below under “—Lone Star’s Reasons for the Lone Star Merger and Recommendation of the Lone Star Board of Directors,” the Lone Star board of directors determined that the Lone Star reorganization agreement and the transactions contemplated thereby were advisable and in the best interests of Lone Star and its shareholders, and unanimously approved the Lone Star reorganization agreement and the transactions contemplated thereby and authorized management to enter into the Lone Star reorganization agreement in the name and on behalf of Lone Star.

In the days following the October 7, 2022 board meeting, representatives of Lone Star and Prosperity continued to discuss the possibility that a regulatory approval could be received subject to a condition requiring one or more divestitures. The parties discussed various alternatives that would provide greater certainty to the parties that the transaction would proceed to closing while equitably allocating the impact of such divestitures among the parties.

On October 10, 2022, the Lone Star board of directors met again with representatives of Stephens and Fenimore to discuss the matter. At the meeting, representatives of Stephens discussed the impact of the proposed

resolution on the financial terms of the transaction, and representatives of Fenimore discussed legal and regulatory matters related to the proposed resolution. Following a lengthy discussion among the Lone Star board of directors, the Lone Star board of directors unanimously agreed to move forward with the Lone Star merger in accordance with its prior authorization.

After this meeting, on October 10, 2022, the parties entered into the Lone Star reorganization agreement, and the directors, executive officers and certain shareholders of Lone Star delivered their respective ancillary agreements to Prosperity and/or Lone Star, as applicable, and the parties announced the transaction in a joint press release prior to the opening of trading on October 11, 2022.

Lone Star’s Reasons for the Lone Star Merger and Recommendation of the Lone Star Board of Directors

The Lone Star board of directors believes that the Lone Star merger is in the best interests of Lone Star and its shareholders. Accordingly, the Lone Star board of directors has unanimously approved the Lone Star reorganization agreement and recommends that the Lone Star shareholders vote “FOR” approval of the Lone Star merger proposal.

In reaching its decision to approve the Lone Star reorganization agreement and to recommend its approval to Lone Star shareholders, the Lone Star board of directors evaluated the Lone Star merger and the Lone Star reorganization agreement in consultation with its executive management, Stephens, Lone Star’s outside financial advisor, and Lone Star’s legal counsel. In arriving at its recommendation, the Lone Star board of directors considered a number of positive factors, including the following:

•

its familiarity with and review of the information concerning the business, results of operations, financial condition, competitive position and future prospects of Lone Star and Prosperity;

•

its knowledge of the current environment in the financial services industry, including national and regional economic conditions, increased regulatory burdens, evolving trends in technology, increasing competition, the current financial market and regulatory conditions and the likely effects of these factors on Lone Star and Prosperity’s potential growth, development, productivity, profitability and strategic options;

•

the complementary aspects of Lone Star’s and Prosperity’s respective businesses, including customer focus, business orientation, employee development and compatibility of the companies’ management and operating styles;

•

the fact that members of senior management of Lone Star are expected to play key leadership roles in Prosperity’s West Texas management team;

•

its belief that a merger with Prosperity would allow Lone Star shareholders to participate in the future performance of a combined company that would have better future prospects and economies of scale than Lone Star was likely to achieve on a stand-alone basis or through other strategic alternatives, and the likely risks and benefits to shareholders of the various strategic options;

•

its belief that Lone Star and Prosperity share a similar strategic vision and a commitment to enhancing the combined bank’s strategic position in Lone Star’s markets;

•

the resources required to keep pace with technology and cybersecurity risks;

•

the financial analyses of Stephens, which were presented to the Lone Star board of directors, and the opinion of Stephens to the effect that, as of October 7, 2022, and subject to the assumptions made, procedures followed, matters considered and limitations and qualifications on the review undertaken by Stephens as described in such written opinion, the Lone Star merger consideration provided under the Lone Star reorganization agreement was fair, from a financial point of view, to the holders of Lone Star common stock, as more fully described below under “—Opinion of Lone Star’s Financial Advisor”;

•

the value of the Lone Star merger consideration compared to, among other metrics: (i) the current and projected book value of Lone Star; (ii) the historical and present operating results of Lone Star; (iii) the estimated future operating results and financial position of Lone Star; and (iv) other similar recent transactions in the industry;

•

its belief that the value of the Lone Star merger consideration to be received by Lone Star’s shareholders under the Lone Star reorganization agreement represents a fair price for the shares of Lone Star’s common stock;

•

the fact that the portion of the Lone Star merger consideration paid in the form of Prosperity common stock would allow former Lone Star shareholders to participate as Prosperity shareholders in the growth of the combined company and in any synergies resulting from the Lone Star merger;

•

the fact that the portion of the Lone Star merger consideration paid in the form of Prosperity common stock is expected to be tax-free to Lone Star shareholders;

•

the historical performance of Prosperity common stock, including historical cash dividends;

•

the limited liquidity that Lone Star shareholders have with respect to their investment in Lone Star, which results not only from the lack of an active public market, but also from the restrictions on transfer resulting from its status as an S corporation, and the fact that as Prosperity shareholders, former Lone Star shareholders would be expected to have materially increased liquidity in the form of a publicly traded NYSE-listed security;

•

the immediate liquidity to Lone Star shareholders, and the certainty of the amount, reflected by the cash portion of the Lone Star merger consideration;

•

the regulatory and other approvals required to complete the Lone Star merger and the likelihood of Prosperity consummating the Lone Star merger and integrating Lone Star’s operations based on Prosperity’s extensive history of successful merger transactions;

•

the potential effect of the Lone Star merger on Lone Star’s employees, including the prospects for continued employment and other benefits agreed to be provided by Prosperity to Lone Star’s employees; and

•

the terms of the Lone Star reorganization agreement, and the presentation of Lone Star’s legal advisors regarding the Lone Star merger and the Lone Star reorganization agreement.

The Lone Star board of directors also considered the risks and potential negative factors outlined below, but concluded that the anticipated benefits of combining with Prosperity were likely to outweigh substantially these risks and factors. These risks included:

•

the potential negative impact of the announcement of the Lone Star merger on Lone Star’s business and relations with customers, service providers and other stakeholders, whether or not the Lone Star merger is completed;

•

the lack of control of the Lone Star board of directors and Lone Star’s shareholders over future operations and strategy of the combined company as compared to remaining independent;

•

the challenges of combining the businesses, assets and workforces of two financial institutions;

•

the potential risk of diverting management focus and resources from other strategic opportunities and from operational matters while working to implement the Lone Star merger;

•

the risks and costs to Lone Star if the Lone Star merger is not completed;

•

the restrictions on the conduct of Lone Star’s business before completion of the Lone Star merger, which may adversely affect Lone Star’s ability to make certain decisions quickly and independently and may delay or prevent Lone Star from undertaking business opportunities that may arise before completion of the Lone Star merger;

•

the possibility that Lone Star may not be able to deliver $121 million in adjusted equity at closing, which would result in a reduction of the Lone Star merger consideration;

•

the fact that the Lone Star merger consideration, a large component of which consists of shares of Prosperity common stock, provides less certainty of value to Lone Star shareholders compared to a transaction in which they would receive all cash consideration;

•

the potential that the value of the Lone Star merger consideration could decline between the date of the Lone Star reorganization agreement and the closing date, reducing the value of the consideration received by Lone Star’s shareholders;

•

the fact that gain on the disposition of Lone Star common stock would generally be taxable to U.S. holders for U.S. federal income tax purposes to the extent of the cash received in the Lone Star merger;

•

the potential for unintended delays in the regulatory approval process;

•

the provisions of the Lone Star reorganization agreement restricting Lone Star’s solicitation of third party acquisition proposals and the fact that Lone Star would be obligated to pay a termination fee, or reimburse certain transaction-related expenses, to Prosperity following the termination of the Lone Star reorganization agreement in certain circumstances; and

•

the interests of certain of Lone Star’s directors and executive officers in the Lone Star merger that are different from, or in addition to, their interests as Lone Star shareholders, which are further described below under “—Financial Interests of Lone Star’s Directors and Executive Officers in the Lone Star Merger” beginning on page 83.

The foregoing discussion of the factors considered by the Lone Star board of directors is not intended to be exhaustive, but is believed to include the material factors considered by the Lone Star board of directors in approving the Lone Star merger. The Lone Star board of directors collectively reached the unanimous conclusion to approve the Lone Star reorganization agreement and the Lone Star merger in light of the various factors described above and other factors that each member of the Lone Star board of directors determined was appropriate. In view of the wide variety of factors considered in connection with its evaluation of the Lone Star merger and the complexity of these matters, the Lone Star board of directors did not find it useful, and did not attempt to quantify, rank or otherwise assign any relative or specific weights to different factors, and individual directors may have given different weights to different factors.

The Lone Star board of directors conducted an overall analysis of the factors described above as a whole, including thorough discussions with, and questioning of, its executive management and outside financial and legal advisors. Based on this analysis, the Lone Star board of directors unanimously determined that the Lone Star reorganization agreement and the Lone Star merger were in the best interests of Lone Star and its shareholders, and approved the Lone Star reorganization agreement and the Lone Star merger.

The foregoing explanation of the Lone Star board of directors’ reasoning and all other information presented in this section is forward-looking in nature and, therefore, should be read in light of the factors discussed in the section entitled “Cautionary Note Regarding Forward-Looking Statements” beginning on page 29.

Each of the directors and certain executive officers of Lone Star, in their capacities as individuals, entered into Lone Star voting agreements with Prosperity and Lone Star pursuant to which they agreed to vote “FOR” the Lone Star merger proposal and “FOR” any other matters required to be approved by the Lone Star shareholders in furtherance of the Lone Star merger proposal. For more information regarding the Lone Star voting agreements, see the section entitled “The Reorganization Agreements—Voting Agreements” beginning on page 107.

LONE STAR’S BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT LONE STAR SHAREHOLDERS VOTE “FOR” THE PROPOSAL TO APPROVE THE LONE STAR REORGANIZATION AGREEMENT AND THE TRANSACTIONS CONTEMPLATED THEREBY.

Prosperity’s Reasons for the Lone Star Merger

As a part of Prosperity’s growth strategy, Prosperity routinely evaluates opportunities to acquire financial institutions. The acquisition of Lone Star is consistent with Prosperity’s expansion strategy. Prosperity’s board of directors, senior management and certain lenders reviewed the business, financial condition, results of operation and prospects for Lone Star, the market condition of the market area in which Lone Star conducts business, the compatibility of the management and the proposed financial terms of the Lone Star merger. In addition, management of Prosperity believes that the Lone Star merger will enhance Prosperity’s presence in the West Texas area, provide opportunities for future growth and provide the potential to realize cost savings. Prosperity’s board of directors also considered the financial condition and valuation for both Lone Star and Prosperity as well as the financial and other effects the Lone Star merger would have on Prosperity’s shareholders.

While management of Prosperity believes that revenue opportunities will be achieved and costs savings will be obtained following the Lone Star merger, Prosperity has not quantified the amount of enhancements or projected the areas of operation in which such enhancements will occur.

In view of the variety of factors considered in connection with its evaluation of the Lone Star merger, the Prosperity board did not find it useful to and did not attempt to quantify, rank or otherwise assign relative weights to factors it considered. Further, individual directors may have given differing weights to different factors. In addition, the Prosperity board did not undertake to make any specific determination as to whether any particular factor, or any aspect of any particular factor, was favorable or unfavorable to its ultimate determination. Rather, the Prosperity board conducted an overall analysis of the factors it considered material, including thorough discussions with, and questioning of, Prosperity’s management.

Opinion of Lone Star’s Financial Advisor

On January 24, 2020, Lone Star engaged Stephens to act as financial adviser to Lone Star in connection with any proposed transaction involving Lone Star and one more parties. As part of its engagement, Stephens assisted Lone Star in connection with the proposed merger of Lone Star with and into Prosperity and was asked by Lone Star to undertake a study of the fairness, from a financial point of view, of the consideration payable in connection with the proposed merger. Lone Star engaged Stephens because, among other factors, Stephens is a nationally recognized investment banking firm with substantial experience in similar transactions. As part of its investment banking business, Stephens is continually engaged in the valuation of financial services businesses and their securities in connection with mergers and acquisitions.

As part of Stephens’ engagement, representatives of Stephens participated in a meeting of the Lone Star board of directors held on October 7, 2022 in which the Lone Star board of directors considered and approved the proposed Lone Star merger. At this meeting, Stephens reviewed the financial aspects of the proposed Lone Star merger and rendered its oral opinion, which was subsequently confirmed by delivery of a written opinion to the Lone Star board of directors dated as of October 7, 2022 that, as of such date, the consideration to be received by the shareholders of Lone Star (solely in their capacity as such) in the proposed Lone Star merger was fair to them from a financial point of view, based upon and subject to the qualifications, assumptions and other matters considered by Stephens in connection with the preparation of its opinion.

The full text of Stephens’ written opinion letter, which we refer to as the “Lone Star Opinion Letter,” is included as Appendix H to this proxy statement/prospectus. The Lone Star Opinion Letter outlines the procedures followed, assumptions made, matters considered and qualifications and limitations on the review undertaken by Stephens in rendering its opinion. The summary of the opinion set forth in this document is qualified in its entirety by reference to the full text of such written Lone Star Opinion Letter. Investors are urged to read the entire Lone Star Opinion Letter carefully in connection with their consideration of the proposed Lone Star merger. Lone Star did not give any instruction to or impose any limitations on Stephens as it related to the issuance of its opinion.

Stephens’ opinion speaks only as of the date of the opinion, and Stephens has undertaken no obligation to update or revise its opinion. The opinion was directed to the Lone Star board of directors (solely in its capacity as such) in connection with, and for purposes of, its consideration of the proposed Lone Star merger. The opinion only addresses whether the consideration to be received by the shareholders of Lone Star (solely in their capacity as such) in the proposed Lone Star merger was fair to them from a financial point of view as of the date of the opinion. The opinion does not address the underlying business decision of Lone Star to engage in the proposed Lone Star merger or any other term or aspect of the Lone Star reorganization agreement or the transactions contemplated thereby. Stephens’ opinion does not constitute a recommendation to the Lone Star board of directors or any of Lone Star’s shareholders as to how such person should vote or otherwise act with respect to the proposed Lone Star merger or any other matter. Lone Star and Prosperity determined the Lone Star merger consideration through a negotiation process.

In connection with developing its opinion, Stephens:

•

reviewed certain publicly available financial statements and reports regarding Lone Star and Prosperity;

•

reviewed certain audited financial statements regarding Lone Star and Prosperity;

•

reviewed certain internal financial statements, management reports and other financial and operating data concerning Lone Star prepared by management of Lone Star;

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reviewed, on a pro forma basis, in reliance upon financial projections and other information and assumptions concerning Lone Star provided by management of Lone Star, and consensus research estimates regarding Prosperity, the effect of the proposed Lone Star merger on the balance sheet, capitalization ratios, earnings and tangible book value both in the aggregate and, where applicable, on a per share basis of Prosperity;

•

reviewed the reported prices and trading activity for the common stock of Prosperity;

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compared the financial performance of Lone Star with that of certain publicly traded companies and their securities that Stephens deemed relevant to Stephens’ analysis of the proposed Lone Star merger;

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reviewed the financial terms, to the extent publicly available, of certain merger or acquisition transactions that Stephens deemed relevant to Stephens’ analysis of the proposed Lone Star merger;

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reviewed the then most recent draft of the Lone Star reorganization agreement and related documents provided to Stephens by Lone Star;

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discussed with management of Lone Star and management of Prosperity the operations of and future business prospects for Lone Star and Prosperity, respectively and the anticipated financial consequences of the proposed Lone Star merger to Lone Star and Prosperity, respectively;

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assisted in Lone Star’s deliberations regarding the material terms of the proposed Lone Star merger and Lone Star’s negotiations with Prosperity; and

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performed such other analyses and provided such other services as Stephens deemed appropriate.

Stephens relied on the accuracy and completeness of the information, financial data and financial forecasts provided to Stephens by Lone Star and Prosperity and of the other information reviewed by Stephens in connection with the preparation of Stephens’ opinion, and its opinion was based upon such information. Stephens did not independently verify or undertake any responsibility to independently verify the accuracy or completeness of any of such information, data or forecasts. Management of Lone Star assured Stephens that it was not aware of any relevant information that had been omitted or remained undisclosed to Stephens. Stephens did not assume any responsibility for making or undertaking an independent evaluation or appraisal of any of the assets or liabilities of Lone Star or of Prosperity, and Stephens was not furnished with any such evaluations or

appraisals; nor did Stephens evaluate the solvency or fair value of Lone Star or of Prosperity under any laws relating to bankruptcy, insolvency or similar matters. Stephens did not assume any obligation to conduct any physical inspection of the properties, facilities, assets or liabilities (contingent or otherwise) of Lone Star or Prosperity. Stephens did not receive or review any individual loan or credit files nor did Stephens make an independent evaluation of the adequacy of the allowance for loan and lease losses of Lone Star or Prosperity. Stephens did not make an independent analysis of the effects of the COVID-19 pandemic, the invasion of Ukraine, potential future changes in the inflation rate or other related market developments or disruptions, or of any other disaster or adversity, on the business or prospects of Lone Star or Prosperity. With respect to the financial forecasts prepared by management of Lone Star and management of Prosperity, including the forecasts of potential cost savings and potential synergies, Stephens assumed that such financial forecasts had been reasonably prepared and reflected the best then currently available estimates and judgments of management of Lone Star and management of Prosperity, respectively, as to the future financial performance of Lone Star and Prosperity, respectively, and provided a reasonable basis for Stephens’ analysis. Stephens recognized that such financial forecasts were based on numerous variables, assumptions and judgments that were inherently uncertain (including, without limitation, factors related to general economic and competitive conditions) and that actual results could vary significantly from such forecasts, and Stephens expressed no opinion as to the reliability of such financial projections and estimates or the assumptions upon which they were based. For a discussion of the financial forecasts and other prospective financial information made available by Lone Star to Stephens for the purpose of Stephens performing its financial analysis in connection with rendering its opinion to the Lone Star board of directors, please see the section entitled “—Certain Unaudited Prospective Financial Information” beginning on page 81.

Stephens does not provide legal, accounting, regulatory, or tax advice or expertise, and Stephens relied solely, and without independent verification, on the assessments of Lone Star and its other advisors with respect to such matters. Stephens assumed, with Lone Star’s consent, that the proposed Lone Star merger will not result in any materially adverse legal, regulatory, accounting or tax consequences for Lone Star or its shareholders and that any reviews of legal, accounting, regulatory or tax issues conducted as a result of the proposed Lone Star merger will be resolved favorably to Lone Star and its shareholders. Stephens did not express any opinion as to any tax or other consequences that might result from the proposed Lone Star merger.

Stephens’ opinion was necessarily based upon market, economic and other conditions as they existed and could be evaluated on the date of the opinion, and on the information made available to Stephens as of the date of the opinion. Market price data used by Stephens in connection with its opinion was based on reported market closing prices as of October 4, 2022. It should be understood that subsequent developments may affect the opinion and that Stephens did not undertake any obligation to update, revise or reaffirm the opinion or otherwise comment on events occurring after the date of the opinion. Stephens further noted that the current volatility and disruption in the credit and financial markets relating to, among other things, the COVID-19 pandemic, the invasion of Ukraine or potential future changes in inflation rates may or may not have an effect on Lone Star or Prosperity, and Stephens did not express an opinion as to the effects of such volatility or such disruption on the proposed Lone Star merger or any party to the proposed Lone Star merger. Stephens further expressed no opinion as to the prices at which shares of Prosperity’s or Lone Star’s common stock may trade at any time subsequent to the announcement of the proposed Lone Star merger.

In connection with developing its opinion, Stephens assumed that, in all respects material to its analyses:

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the proposed Lone Star merger and any related transactions will be consummated on the terms of the latest draft of the Lone Star reorganization agreement provided to Stephens, without material waiver or modification;

•

the representations and warranties of each party in the Lone Star reorganization agreement and in all related documents and instruments referred to in the Lone Star reorganization agreement are true and correct;

•

each party to the Lone Star reorganization agreement and all related documents will perform all of the covenants and agreements required to be performed by such party under such documents;

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all conditions to the completion of the proposed Lone Star merger will be satisfied within the time frames contemplated by the Lone Star reorganization agreement without any waivers;

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that in the course of obtaining the necessary regulatory, lending or other consents or approvals (contractual or otherwise) for the proposed Lone Star merger and any related transactions, no restrictions, including certain divestiture requirements, or amendments or modifications, will be imposed that would have a material adverse effect on the contemplated benefits of the proposed Lone Star merger to the shareholders of Lone Star;

•

there has been no material change in the assets, liabilities, financial condition, results of operations, business or prospects of Lone Star or Prosperity since the date of the most recent financial statements made available to Stephens, and that no legal, political, economic, regulatory or other development has occurred that will adversely impact Lone Star or Prosperity; and

•

the proposed Lone Star merger will be consummated in a manner that complies with applicable law and regulations.

Stephens’ opinion was limited to whether the consideration to be received by the shareholders of Lone Star (solely in their capacity as such) in the proposed Lone Star merger was fair to them from a financial point of view as of the date of the opinion. Stephens was not asked to, and it did not, offer any opinion as to the terms of the Lone Star reorganization agreement or the form of the proposed Lone Star merger or any aspect of the proposed Lone Star merger, other than the fairness, from a financial point of view, of the consideration to be received in the proposed Lone Star merger by the shareholders of Lone Star (solely in their capacity as such). The opinion did not address the merits of the underlying decision by Lone Star to engage in the proposed Lone Star merger, the merits of the proposed Lone Star merger as compared to other alternatives potentially available to Lone Star or the relative effects of any alternative transaction in which Lone Star might engage, nor is it intended to be a recommendation to any person or entity as to any specific action that should be taken in connection with the proposed Lone Star merger, including with respect to how to vote or act with respect to the proposed Lone Star merger. Moreover, Stephens did not express any opinion as to the fairness of the amount or nature of the compensation to any of Lone Star’s officers, directors or employees, or to any group of such officers, directors or employees, whether relative to the compensation to other shareholders of Lone Star or otherwise.

The following is a summary of the material financial analyses performed and material factors considered by Stephens in connection with developing its opinion. Stephens performed certain procedures, including each of the financial analyses described below, and reviewed with Lone Star’s executive management and board of directors the assumptions upon which the analyses were based, as well as other factors. Although this summary does not purport to describe all of the analyses performed or factors considered by Stephens, it does set forth those analyses considered by Stephens to be material in arriving at its opinion. The preparation of a fairness opinion is a complex analytic process involving various determinations as to the appropriate and relevant methods of financial analysis and the application of those methods to the particular circumstances. Therefore, a fairness opinion is not readily susceptible to partial analysis or summary description. The order of the summaries of analyses described does not represent the relative importance or weight given to those analyses by Stephens. It should be noted that in arriving at its opinion, Stephens did not attribute any particular weight to any analysis or factor considered by it, but rather made qualitative judgments as to the significance and relevance of each analysis and factor. Accordingly, Stephens believes that its analysis must be considered as a whole and that considering any portion of such analyses and factors, without considering all analyses and factors as a whole, could create a misleading or incomplete view of the process underlying its opinion. The financial analyses summarized below include information presented in tabular format. The tables alone do not constitute a complete description of the financial analyses summarized below. Accordingly, Stephens’ analyses and the summary of its analyses must be considered as a whole, and selecting portions of its analyses and factors or focusing on the information presented below in tabular format, without considering all analyses and factors or the full narrative description of the financial analyses, including the methodologies and assumptions underlying the analyses, could create a misleading or incomplete view of the process underlying Stephens’ analyses and opinion.

Summary of Proposed Lone Star Merger

Pursuant to the Lone Star reorganization agreement, and subject to the terms, conditions and limitations set forth therein, and for purposes of its opinion, Stephens understood that, subject to potential adjustments as described in the Lone Star reorganization agreement, the consideration expected to be exchanged by Prosperity for all of the outstanding common stock, stock appreciation rights and options on the common stock of Lone Star has an aggregate value of approximately $234.4 million and will consist of 2,376,182 shares of Prosperity’s common stock and $64,053,717 in cash. Stephens further understood that under the Lone Star reorganization agreement each share of Lone Star’s outstanding common stock will be entitled to receive approximately 0.3968 shares of Prosperity’s common stock and approximately $9.19 in cash, based on Prosperity’s closing stock price as of October 4, 2022, and the outstanding stock appreciation rights and options on Lone Star’s common stock will be entitled to receive cash in connection with the closing of the Lone Star reorganization agreement and will be terminated. Based upon the unaudited financial information of Lone Star of and for the twelve months ended June 30, 2022, and market data as of October 4, 2022, Stephens calculated the following transaction multiples:


Transaction Value / Reported Tangible Book Value	1.94x
Transaction Value / Adjusted Tangible Book Value (9.0%)	1.97x
Transaction Value / Last Twelve Months Earnings⁽¹⁾	14.9x
Core Deposit Premium	12.3	%

Note: The last twelve months earnings of Lone Star is based on the most recent available financial statements prior to announcement of the Lone Star merger.

⁽¹⁾	Reflects 21% tax effect due to subchapter S corporate status.

Relevant Public Companies Analysis

Stephens compared the financial condition, operating statistics and market valuation of Lone Star to certain public companies selected by Stephens and their respective public trading values. Stephens selected the companies outlined below because their relative asset size and financial performance, among other factors, were reasonably similar to Lone Star; however, no selected company below was identical or directly comparable to Lone Star. A complete analysis involves complex considerations and qualitative judgments concerning differences in financial and operating characteristics and other factors that could affect the public trading values of the relevant public companies. Mathematical analysis (such as determining the median) is not in itself a meaningful method of using relevant public company data.

Stephens selected the following public companies based on the criteria set forth below:

Includes nationwide major exchange traded banks between $1.0 billion and $2.5 billion in total assets, a last twelve months return on average assets greater than 1.20%, a nonperforming assets to total assets ratio less than 1.00%, and a loans to deposits ratio less than 100%.


• Citizens & Northern Corporation		• OP Bancorp

• PCB Bancorp		• MainStreet Bancshares, Inc.

• John Marshall Bancorp, Inc.		• First United Corporation

• Citizens Financial Services, Inc.		• National Bankshares, Inc.

• Capital Bancorp, Inc.		• FNCB Bancorp, Inc.

• Norwood Financial Corp.		• Plumas Bancorp

• USCB Financial Holdings, Inc.		• Bank7 Corp.

• Parke Bancorp, Inc.


	Lone Star			25^th Percentile			Median			75^th Percentile
Total Assets (in billions)	$	1.3		$	1.7		$	2.0		$	2.2
Tangible Common Equity / Total Assets		9.3	%		7.4	%		8.6	%		8.9	%
Price / Tangible Book Value		1.94x			1.09x			1.50x			1.68x
Price / Adj. Tangible Book Value (9.0%)		1.97x			1.07x			1.42x			1.62x
Price / Last Twelve Months Net Income ⁽¹⁾		14.9x			7.0x			8.1x			9.5x

Source: S&P Capital IQ Pro and FactSet.

⁽¹⁾	Lone Star multiple reflects 21% tax effect due to subchapter S corporate status.

Discounted Cash Flow Analysis

Stephens performed a standalone discounted cash flow analysis using projections developed by the executive management team of Lone Star and then calculated a range of implied equity values for Lone Star based upon the discounted net present value of the projected after-tax free cash flows for the projected period. Stephens determined the amount of cash flow assuming (i) a terminal earnings multiple of 9.0x, (ii) dividend payments for earnings and excess capital above a tangible common equity to tangible asset ratio of 9.0% from 2022 to 2026 and (iii) the present value of Lone Star’s implied standalone terminal values at the end of such period. Stephens calculated the terminal values of Prosperity based on 2027 estimated earnings and multiples of 8.0x to 10.0x. Stephens considered discount rates from 11.0% to 13.0% for Lone Star. Based on this analysis, Stephens derived a range for the implied equity value of Lone Star from $31.75 per share to $39.34 per share.

The discounted cash flow analysis is a widely used valuation methodology, but the results of this methodology are highly dependent on the assumptions that must be made, including asset and earnings growth rates, terminal values, capital levels, and discount rates. The analysis did not purport to be indicative of the actual values or expected values of Lone Star. The actual results may vary from the projected results, any of these assumptions might not be realized in future operations and the variations may be material. For a discussion of the financial forecasts and other prospective financial information made available by Lone Star to Stephens for the purpose of Stephens performing its financial analysis in connection with rendering its opinion to the Lone Star board of directors, please see the section entitled “—Certain Unaudited Prospective Financial Information” beginning on page 81.

Relevant Nationwide Transactions Analysis

Stephens reviewed certain publicly available transaction multiples and related financial data for transactions nationwide announced since 2020, where (i) the deal value was publicly disclosed, (ii) the target’s assets were between $1.0 billion and $1.5 billion, (iii) the target’s last twelve months return on average assets was greater than 1.00%, (iv) the target’s nonperforming assets to total assets ratio was less than 1.00% and (v) the target’s tangible common equity to tangible assets ratio was greater than 8.00% (excluding any Merger of Equals (as defined by S&P Global Market Intelligence)). The following transactions were selected by Stephens because each target’s relative asset size, financial performance and operations, among other factors, was reasonably similar to Lone Star; however, no selected company or transaction below was identical or directly comparable to Lone Star or the proposed Lone Star merger (in each transaction, the acquirer is listed first and the target is listed second):

•

Seacoast Banking Corporation of Florida/Drummond Banking Company

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Nicolet Bankshares, Inc./Charter Bankshares, Inc.

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German American Bancorp, Inc./Citizens Union Bancorp of Shelbyville, Inc.

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CVB Financial Corp./Suncrest Bank

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Valley National Bancorp/The Westchester Bank Holding Corporation

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Simmons First National Corporation/Landmark Community Bank

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Enterprise Financial Services Corp/Seacoast Commerce Banc Holdings

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Business First Bancshares, Inc./Pedestal Bancshares, Inc.

Stephens considered these selected transactions to be reasonably similar, but not identical or directly comparable, to the proposed Lone Star merger. A complete analysis involves complex considerations and qualitative judgments concerning differences in the selected transactions and other factors that could affect the transaction values in those selected transactions as compared with the proposed Lone Star merger. Mathematical analysis (such as determining the median) is not in itself a meaningful method of using selected transaction data. Stephens compared certain proposed transaction multiples of the proposed Lone Star merger to the 25^th percentile, median and 75^th percentile transaction multiples of the selected transactions:


	Lone Star			25^th Percentile			Median			75^th Percentile
Deal Value (in millions)	$	234		$	157		$	166		$	206
Target Total Assets (in billions)	$	1.3		$	1.1		$	1.2		$	1.3
Target Tangible Common Equity / Total Assets		9.3	%		8.7	%		9.6	%		10.1	%
Target Last Twelve Months Return on Average Assets		1.26	%		1.08	%		1.24	%		1.32	%
Transaction Value / Tangible Book Value		1.94x			1.51x			1.56x			1.69x
Transaction Value / Adj. Tangible Book Value (9.0%)		1.97x			1.55x			1.62x			1.70x
Transaction Value / Last Twelve Months Earnings⁽¹⁾		14.9x			12.2x			13.2x			14.1x
Core Deposit Premium		12.3	%		6.4	%		7.9	%		8.8	%

Source: S&P Capital IQ Pro, Lone Star management and draft Lone Star reorganization agreement.

⁽¹⁾	Lone Star multiple reflects 21% tax effect due to subchapter S corporate status.

Relevant Texas Transactions Analysis

Stephens reviewed certain publicly available transaction multiples and related financial data for transactions with a target headquarters domiciled in Texas announced since 2020, where (i) the deal value was publicly disclosed, and (ii) the target’s assets were between $500 million and $10 billion (excluding any Merger of Equals (as defined by S&P Global Market Intelligence)). The following transactions were selected by Stephens because each target’s relative asset size, financial performance and markets of operation, among other factors, was reasonably similar to Lone Star; however, no selected company or transaction below was identical or directly comparable to Lone Star or the proposed Lone Star merger (in each transaction, the acquirer is listed first and the target is listed second):

•

Origin Bancorp, Inc./BT Holdings, Inc.

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Simmons First National Corporation/Spirit of Texas Bancshares, Inc.

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Business First Bancshares, Inc./Texas Citizens Bancorp, Inc.

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Home Bancshares, Inc./Happy Bancshares, Inc.

•

BancorpSouth Bank/National United Bancshares, Inc.

•

Heartland Financial USA, Inc./AIM Bancshares, Inc.


	Lone Star			25^th Percentile			Median			75^th Percentile
Deal Value (in millions)	$	234		$	156		$	297		$	515
Target Total Assets (in billions)	$	1.3		$	1.0		$	1.9		$	2.9
Target Tangible Common Equity / Total Assets		9.3	%		8.1	%		9.5	%		10.2	%
Target Last Twelve Months Return on Average Assets		1.26	%		1.15	%		1.28	%		1.39	%
Transaction Value / Tangible Book Value		1.94x			1.56x			1.58x			1.77x
Transaction Value / Adj. Tangible Book Value (9.0%)		1.97x			1.60x			1.63x			1.87x
Transaction Value / Last Twelve Months Earnings⁽¹⁾		14.9x			12.7x			13.6x			15.3x
Core Deposit Premium		12.3	%		6.9	%		7.6	%		11.2	%

Source: S&P Capital IQ Pro, Lone Star management and draft Lone Star reorganization agreement.

⁽¹⁾	Lone Star multiple reflects 21% tax effect due to subchapter S corporate status.

Miscellaneous

In performing its analyses, Stephens made numerous assumptions with respect to industry performance, general business, economic and regulatory conditions and other matters, many of which are beyond the control of Lone Star. The analyses performed by Stephens are not necessarily indicative of actual values, trading values or actual future results which might be achieved, all of which may be significantly more or less favorable than suggested by such analyses. The analyses do not purport to be appraisals or to reflect the prices at which companies may actually be sold, and such estimates are inherently subject to uncertainty.

Stephens is serving as financial adviser to Lone Star in connection with the proposed Lone Star merger and is entitled to receive from Lone Star reimbursement of its expenses and a fee for its services as financial advisor to Lone Star, a significant portion of which is contingent upon the consummation of the proposed Lone Star merger. Stephens also received a fee from Lone Star upon rendering its fairness opinion, which opinion fee will be credited in full against the fee which will become payable to Stephens upon the closing of the proposed Lone Star merger. Lone Star has also agreed to indemnify Stephens against certain claims and liabilities that could

arise out of Stephens’ engagement, including certain liabilities that could arise out of Stephens’ providing its opinion.

Stephens issues periodic research reports regarding the business and prospects of Prosperity, and Stephens makes a market in the stock of Prosperity. Stephens has not received fees for providing investment banking services to Lone Star or Prosperity within the past two years. Stephens expects to pursue future investment banking services assignments with participants in the proposed Lone Star merger transaction.

Certain Unaudited Prospective Financial Information

Prosperity and Lone Star do not as a matter of course make public projections as to future performance, revenues, earnings or other financial results due to, among other reasons, the inherent uncertainty of the underlying assumptions and estimates of any such projections. However, Lone Star is including in this proxy statement/prospectus certain unaudited prospective financial information that was made available by Lone Star to Stephens for the purpose of Stephens performing its financial analysis in connection with rendering its opinion to the Lone Star board of directors, as described above under the section entitled “—Opinion of Lone Star’s Financial Advisor.” This unaudited prospective financial information was provided by Lone Star management and was not prepared, provided to, reviewed or approved by Prosperity management or the Prosperity board of directors. By inclusion of this information, the respective managements and boards of directors of Prosperity and Lone Star and Lone Star’s financial advisor, assume no responsibility for the unaudited prospective financial information. The inclusion of this information should not be regarded as an indication that any of Prosperity, Lone Star, Stephens, their respective representatives or any other recipient of this information considered, or now considers, it to be necessarily predictive of actual future results, or that it should be construed as financial guidance, and it should not be relied on as such.

The information regarding Lone Star below was provided by Lone Star management for internal use and is subjective in many respects. While presented with numeric specificity, the unaudited prospective financial information reflects numerous estimates and assumptions made by Lone Star management with respect to business, economic, market, competition, regulatory and financial conditions and matters specific to Lone Star’s business, all of which are difficult to predict and many of which are beyond Lone Star’s control. The unaudited prospective financial information of Lone Star reflects both assumptions by Lone Star management as to certain business decisions that are subject to change and, in many respects, subjective judgment by Lone Star management, and thus is susceptible to multiple interpretations and periodic revisions based on actual experience and business developments. No assurance can be given that the unaudited prospective financial information and the underlying estimates and assumptions will be realized. Actual results may differ materially from those set forth below, and important factors that may affect actual results and cause the unaudited prospective financial information to be inaccurate include, but are not limited to, risks and uncertainties relating to Lone Star’s business, industry performance, general business and economic conditions, competition, customer requirements and adverse changes in applicable laws, regulations or rules. For other factors that could cause actual results to differ, see the sections entitled “Risk Factors” beginning on page 33 and “Cautionary Note Regarding Forward-Looking Statements” beginning on page 29.

The unaudited prospective financial information was not provided by Lone Star management with a view toward public disclosure, nor was it prepared with a view toward compliance with GAAP, the prevailing practices in the banking industry, published guidelines of the SEC or the guidelines established by the American Institute of Certified Public Accountants for preparation and presentation of prospective financial information. In addition, the unaudited prospective financial information requires significant estimates and assumptions that make it inherently less comparable to the similarly titled GAAP measures in Prosperity’s and Lone Star’s

respective historical GAAP financial statements. Neither Prosperity’s nor Lone Star’s independent public accountants nor any other independent accountants, have compiled, examined or performed any procedures with respect to the unaudited prospective financial information contained herein, nor have they expressed any opinion or any other form of assurance on such information or its achievability.

Furthermore, the unaudited prospective financial information does not take into account any circumstances or events occurring after the date it was prepared. No assurance can be given that, had the unaudited prospective financial information been prepared as of the date of this proxy statement/prospectus, similar estimates and assumptions would be used. Neither Prosperity nor Lone Star intends to, and expressly disclaims any obligation to, make publicly available any update or other revision to the unaudited prospective financial information to reflect circumstances existing since their preparation or to reflect the occurrence of unanticipated events, even in the event that any or all of the underlying assumptions are shown to be in error, or to reflect changes in general economic or industry conditions. The unaudited prospective financial information does not take into account the possible financial and other effects of the Lone Star merger and does not attempt to predict or suggest future results of the surviving company. The unaudited prospective financial information of Lone Star is presented strictly on a stand-alone basis and does not give effect to the Lone Star merger, including the impact of negotiating or executing the Lone Star reorganization agreement, the expenses that may be incurred in connection with consummating the Lone Star merger, the potential synergies that may be achieved by the surviving company as a result of the Lone Star merger, the effect on Lone Star of any business or strategic decision or action that has been or will be taken as a result of the Lone Star reorganization agreement having been executed, or the effect of any business or strategic decisions or actions that would likely have been taken if the Lone Star reorganization agreement had not been executed, but which were instead altered, accelerated, postponed or not taken in anticipation of the Lone Star merger. Further, the unaudited prospective financial information does not take into account the effect on Lone Star of any possible failure of the Lone Star merger to occur.

None of Prosperity, Lone Star, Stephens, or their respective affiliates, officers, directors, advisors or other representatives has made, makes or is authorized in the future to make any representation to any shareholder of Prosperity or Lone Star or other persons regarding Lone Star’s ultimate performance compared to the information contained in the unaudited prospective financial information or that the projected results will be achieved. The summary of the unaudited prospective financial information included below is not being included to influence your decision whether to vote for the Lone Star merger proposal, but is being provided solely because it was made available to Stephens in connection with the Lone Star merger.

In light of the foregoing, and considering that the Lone Star special meeting will be held many months after the unaudited prospective financial information was prepared, as well as the uncertainties inherent in any forecasted information, Lone Star shareholders are cautioned not to place unwarranted reliance on such information, and all Lone Star shareholders are urged to review the other information contained elsewhere in this proxy statement/prospectus for a description of Prosperity’s and Lone Star’s respective businesses, as well as Prosperity’s most recent SEC filings for a description of its reported financial results. See the section entitled “Where You Can Find More Information” beginning on page 141.

The following table presents selected unaudited prospective financial data of Lone Star on a stand-alone basis and were provided by Lone Star management for Stephens’ financial analysis in connection with rendering its opinion to the Lone Star board of directors, as described in this proxy statement/prospectus under the section entitled “—Opinion of Lone Star’s Financial Advisor.”


	As of or For the Years Ended December 31,
	2022		2023		2024		2025		2026
Lone Star Net Income (in millions)	$	20.3	$	24.2	$	25.6	$	27.2	$	28.8
Lone Star Total Assets (in billions)		1.3		1.4		1.5		1.6		1.7


		Assumed Long-Term Growth Rates for Lone Star
Earnings (%)		6.0%
Total Assets (%)		6.0%

Financial Interests of Lone Star’s Directors and Executive Officers in the Lone Star Merger

In the Lone Star merger, the directors and executive officers of Lone Star will receive the same consideration for their shares of Lone Star common stock as all other Lone Star shareholders. In considering the recommendation of the Lone Star board of directors that you vote “FOR” the Lone Star merger proposal, you should be aware that some of Lone Star’s executive officers and directors have interests in the Lone Star merger, which may be considered to be different from, or in addition to, the interests of the Lone Star shareholders generally. These interests are described below. The Lone Star board of directors was aware of these interests and considered them, among other matters, in reaching its decision to unanimously approve the Lone Star reorganization agreement, the Lone Star merger and the other transactions contemplated by the Lone Star reorganization agreement and recommend that Lone Star shareholders vote “FOR” the Lone Star merger proposal.

Employment Agreements with Prosperity

As a material inducement to Prosperity to enter into the Lone Star reorganization agreement, Prosperity Bank entered into employment agreements with certain of the executive officers of Lone Star, including Alan Lackey and Melisa Roberts, which are designed to govern the terms and conditions of each such individual’s service relationship with Prosperity Bank following the effective time of the Lone Star merger. Each agreement is for an initial term of three years, entitles the named individual to receive a base annual salary over the term of the agreement, sets forth the eligibility terms for bonuses and provides for participation in certain employee benefit plans and stock based compensation programs of Prosperity, among other things. Each agreement also sets forth the conditions under which the agreement may be terminated and contains non-competition and non-solicitation obligations for a specified period of time.

Acceleration of Equity Awards

At the Lone Star effective time, subject to the terms and conditions of the Lone Star reorganization agreement, each option granted by Lone Star to purchase shares of Lone Star common stock or stock appreciation rights granted under the Lone Star equity compensation plans will fully vest and be cancelled and converted into the right to receive a cash payment equal to the difference between the per award share merger consideration (as defined in the Lone Star reorganization agreement) and the per share exercise price of such for each share of Lone Star common stock subject to such Lone Star stock option or the initial value of such stock appreciation right, as applicable. The following table sets forth the stock options held by the Lone Star directors and executive officers as of the Lone Star record date:


Name of Optionholder	Number of Vested Options		Number of Non-Vested Options
Clifton E. Bickerstaff		—		—
Frosty Gilliam, Jr.		—		—
Lestie Glover		6,800		—
Mark S. Hallgren		3,000		—
Alan L. Lackey		—		—
Edmund W. McGee		6,800		—
Charles E. Needham		—		—
William Wade Porter		—		—
Melisa Roberts		7,500		—
Brent Wade		—		—

The following table sets forth holdings of stock appreciation rights by the Lone Star directors and executive officers as of the Lone Star record date:


Name of SAR Holder	Number of Vested SARs		Number of Non-Vested SARs
Clifton E. Bickerstaff		—		6,000
Frosty Gilliam, Jr.		11,000		—
Lestie Glover		9,000		12,000
Mark S. Hallgren		5,000		6,000
Alan L. Lackey		5,000		10,000
Edmund W. McGee		21,000		—
Charles E. Needham		5,000		6,000
William Wade Porter		5,000		6,000
Melisa Roberts		12,000		15,000
Brent Wade		—		6,000

Change in Control Payments

Lone Star is a party to change in control agreements with certain of its executive officers who are not under employment agreements discussed above, which provide, among other things, for change in control payments following the completion of the Lone Star merger. Under the terms of the Lone Star reorganization agreement, the after-tax amount of the change in control payments must be paid or properly accrued for by Lone Star for purposes of calculating its closing equity capital. The aggregate amount of the change in control payments that are expected to be paid to such individuals following the completion of the Lone Star merger is approximately $1.5 million.

Indemnification

The Lone Star reorganization agreement provides that Prosperity will indemnify each director and officer of Lone Star or Lone Star Bank as of the effective time of the Lone Star merger for a period of four years thereafter, against any costs or expenses (including reasonable attorneys’ fees), judgments, fines, losses, claims, damages or liabilities incurred in connection with any claim, action, suit, proceeding or investigation, whether civil, criminal, administrative or investigative, arising out of matters existing or occurring at or before the effective time of the merger, whether asserted or claimed before, at or after the effective time of the Lone Star merger, arising in whole or in part out of or pertaining to the fact that he or she was acting in his or her capacity as a director or officer of Lone Star or Lone Star Bank to the fullest extent that the indemnified party would be entitled under Lone Star’s certificate of formation or bylaws or the similar constituent documents of Lone Star Bank, as applicable, as in effect on the date of the reorganization agreement and to the extent permitted by applicable law.

THE MERGERS

Board of Directors and Management of Prosperity and Prosperity Bank After the Mergers

The directors and officers of Prosperity and Prosperity Bank immediately prior to the effective time of each of the mergers will serve as the directors and officers of the surviving corporation and surviving bank from and after the effective time of each of the mergers in accordance with the bylaws of the surviving corporation and surviving bank. Information about the current members of the Prosperity board of directors can be found in the documents listed in the section entitled “Where You Can Find More Information” beginning on page 141.

Public Trading Markets

Prosperity common stock is listed on the NYSE under the symbol “PB.” The Prosperity common stock issuable in the mergers will be listed on the NYSE.

Under the reorganization agreements, Prosperity has agreed to file all documents required to be filed to have the shares of Prosperity common stock to be issued in each merger approved for listing on the NYSE prior to the closing of such merger and to use its commercially reasonable efforts to effect such listing. The obligations of the parties to complete each merger are subject to such shares having been approved for listing on the NYSE and such approval having not been withdrawn or revoked.

Dissenters’ Rights of Appraisal

General. If you hold one or more shares of First Bancshares common stock or Lone Star common stock, as applicable, you are entitled to dissenters’ rights under Texas law and have the right to dissent from the applicable merger and have the appraised fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable, paid to you in cash. The appraised fair value may be more or less than the value of the shares of Prosperity common stock and cash being paid in the applicable merger. If you are contemplating exercising your right to dissent, we urge you to read carefully the provisions of Chapter 10, Subchapter H of the TBOC, which are attached to this proxy statement/prospectus as Appendix I, and consult with your legal counsel before electing or attempting to exercise these rights. The following discussion describes the steps you must take if you want to exercise your right to dissent. You should read this summary and the full text of the law carefully.

How to Exercise and Perfect Your Right to Dissent. To be eligible to exercise your right to dissent to the First Bancshares merger or the Lone Star merger, as applicable:

•

you must, prior to the First Bancshares special meeting or the Lone Star special meeting, as applicable, provide First Bancshares or Lone Star, as applicable, with a written objection to the applicable merger that states that you will exercise your right to dissent if the applicable merger is completed and that provides an address to which Prosperity may send a notice if the applicable merger is completed;

•

you must vote your shares of First Bancshares common stock or Lone Star common stock, as applicable, against the applicable reorganization agreement;

•

you must, not later than the 20th day after Prosperity sends you notice that the applicable merger was completed, provide Prosperity with a written demand for payment that states the number and class of shares of First Bancshares capital stock or Lone Star capital stock, as applicable, you own, your estimate of the fair value of such stock and an address to which a notice relating to the dissent and appraisal procedures may be sent; and

•

you must, not later than the 20th day after the date on which you make written demand for payment, submit to Prosperity your certificates representing First Bancshares common stock or Lone Star common stock, as applicable, to which the demand relates for purposes of making a notation on the certificates that a demand for the payment of the fair value of your certificates representing First Bancshares common stock or Lone Star common stock, as applicable, has been made.

If you intend to dissent from the First Bancshares merger or the Lone Star merger, you must send the notice to the applicable party at the proper address below:

First Bancshares of Texas, Inc.

310 West Wall Street, Suite 1200

Midland, Texas 79701

Attention: Robin Richey

Telephone: (432) 687-9102

Email: rrichey@fcbtexas.com

Lone Star State Bancshares, Inc.

6220 Milwaukee Avenue

Lubbock, Texas 79424

Attention: Alan Lackey

Telephone: (806) 771-7717

Email: alanlackey@lonestarwtx.com

If you fail to vote your shares of First Bancshares common stock or Lone Star common stock at the applicable special meeting against the approval of the applicable reorganization agreement, you will lose your right to dissent from the applicable merger. You will instead receive shares of Prosperity common stock and cash as described in the applicable reorganization agreement. If you comply with the first two items above and the First Bancshares merger or the Lone Star merger, as applicable, is completed, Prosperity will send you a written notice advising you that the applicable merger has been completed. Prosperity must deliver this notice to you within ten days after the applicable merger is completed.

Your Demand for Payment. If you wish to receive the fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable, in cash, you must, within 20 days of the date the notice was delivered or mailed to you by Prosperity, send a written demand to Prosperity for payment of the fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable. The fair value of your shares of First Bancshares common stock or Lone Star common stock will be the value of the shares on the day immediately preceding the applicable merger, excluding any appreciation or depreciation in anticipation of the applicable merger. Your written demand and any notice addressed to Prosperity must be sent to:

Prosperity Bancshares, Inc.

Prosperity Bank Plaza

4295 San Felipe

Houston, Texas 77027

Attention: President and Secretary

Your written demand must state how many shares of First Bancshares common stock or Lone Star common stock, as applicable, you own and your estimate of the fair value of your shares of First Bancshares common stock or Lone Star common stock. If you fail to send this written demand to Prosperity within 20 days of Prosperity’s delivery or mailing of your notice, you will be bound by the applicable merger and you will not be entitled to receive a cash payment representing the fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable. Instead, you will receive shares of Prosperity common stock and cash as described in the applicable reorganization agreement.

In addition, not later than the 20th day after the date on which you make written demand for payment, you must submit to Prosperity your certificates representing First Bancshares common stock or Lone Star common stock, as applicable, to which the demand relates for purposes of making a notation on the certificates that a demand for the payment of the fair value of your certificates representing First Bancshares common stock or Lone Star common stock, as applicable, has been made. If you fail to submit your certificates within the required period, it will have the effect of terminating, at the option of Prosperity, your right to dissent and appraisal unless a court, for good cause shown, directs otherwise.

Prosperity’s Actions Upon Receipt of Your Demand for Payment. Within 20 days after Prosperity receives your demand for payment and your estimate of the fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable, Prosperity must send you written notice stating whether or not it accepts your estimate of the fair value of your shares.

If Prosperity accepts your estimate, Prosperity will notify you that it will pay the amount of your estimated fair value within 90 days of the applicable merger being completed. Prosperity will make this payment to you only if you have surrendered the share certificates representing your shares of First Bancshares common stock or Lone Star common stock, as applicable, duly endorsed for transfer, to Prosperity.

If Prosperity does not accept your estimate, Prosperity will notify you of this fact and will make an offer of an alternative estimate of the fair value of your shares that it is willing to pay you within 120 days of the applicable merger being completed, which you may accept within 90 days or decline.

Payment of the Fair Value of Your Shares of First Bancshares Common Stock or Lone Star Common Stock Upon Agreement of an Estimate. If you and Prosperity have reached an agreement on the fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable, within 90 days after the applicable merger is completed, Prosperity must pay you the agreed amount within 120 days after the applicable merger is completed, provided that you have surrendered the share certificates representing your shares of First Bancshares common stock or Lone Star common stock, as applicable, duly endorsed for transfer, to Prosperity.

Commencement of Legal Proceedings if a Demand for Payment Remains Unsettled. If you and Prosperity have not reached an agreement as to the fair market value of your shares of First Bancshares common stock or Lone Star common stock, as applicable, within 90 days after the applicable merger is completed, you or Prosperity may, within 60 days after the expiration of the 90-day period, commence proceedings in Harris County, Texas, asking the court to determine the fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable. The court will determine if you have complied with the dissent provisions and if you have become entitled to a valuation of and payment for your shares of First Bancshares common stock or Lone Star common stock, as applicable. The court will appoint one or more qualified persons to act as appraisers to determine the fair value of your shares. The appraisers will determine the fair value of your shares and will report this value to the court. The court will consider the report, and both you and Prosperity may address the court about the report. The court will determine the fair value of your shares and direct Prosperity to pay that amount, plus interest, which will begin to accrue 91 days after the applicable merger is completed.

Rights as a Shareholder. If you have made a written demand on Prosperity for payment of the fair value of your shares of First Bancshares common stock or Lone Star common stock, as applicable, you will not thereafter be entitled to vote or exercise any other rights as a shareholder except the right to receive payment for your shares as described herein and the right to maintain an appropriate action to obtain relief on the ground that the applicable merger would be or was fraudulent. In the absence of fraud in the transaction, your right under the dissent provisions described herein is the exclusive remedy for the recovery of the value of your shares or money damages with respect to the First Bancshares merger or the Lone Star merger, as applicable.

Withdrawal of Demand. If you have made a written demand on Prosperity for payment of the fair value of your First Bancshares common stock or Lone Star common stock, as applicable, you may withdraw such demand at any time before payment for your shares has been made or before a petition has been filed with a court for determination of the fair value of your shares. If you withdraw your demand or are otherwise unsuccessful in asserting your dissenters’ rights, you will be bound by the applicable merger and your status as a shareholder will be restored without prejudice to any corporate proceedings, dividends or distributions which may have occurred during the interim.

Regulatory Approvals Required for the Mergers

The completion of the First Bancshares merger is subject to (i) waiver by the Federal Reserve Board of the application and prior approval requirements of the Bank Holding Company Act with respect to the merger of

First Bancshares with and into Prosperity, and (ii) receipt of the approval of each of the FDIC and the TDB with respect to the merger of FirstCapital Bank with and into Prosperity Bank.

The completion of the Lone Star merger is subject to (i) waiver by the Federal Reserve Board of the application and prior approval requirements of the Bank Holding Company Act with respect to the merger of Lone Star with and into Prosperity, and (ii) receipt of the approval of each of the FDIC and the TDB with respect to the merger of Lone Star Bank with and into Prosperity Bank.

On November 18, 2022 and November 21, 2022, Prosperity filed the required documentation with the Federal Reserve Bank of Dallas to request a waiver of its approval with respect to the Lone Star merger and the First Bancshares merger, respectively.

On November 16, 2022, Prosperity Bank and Lone Star Bank filed the required applications with the FDIC and TDB; and on November 17, 2022, Prosperity Bank and FirstCapital Bank filed the required applications with the FDIC and the TDB to obtain approval of the respective bank mergers. Each application is pending.

In addition to the FDIC, the Antitrust Division of the Department of Justice, or the “DOJ,” conducts a concurrent competitive review of the mergers to analyze each merger’s competitive effects and determine whether either merger would result in a violation of antitrust laws. Transactions approved under the Federal Deposit Insurance Act generally may not be completed until 30 days after the approval of the applicable federal banking agency is received, during which time the DOJ may challenge the transaction on antitrust grounds. With the approval of the applicable federal banking agency and the concurrence of the DOJ, the waiting period may be reduced to no less than 15 days. The commencement of an antitrust action would stay the effectiveness of such an approval unless a court specifically ordered otherwise. In reviewing the mergers, the DOJ could analyze each merger’s effect on competition differently than the FDIC and, thus, it is possible that the DOJ could reach a different conclusion than the FDIC regarding the effects of each merger on competition. A determination by the DOJ not to object to the mergers may not prevent the filing of antitrust actions by private persons or state attorneys general. There can be no assurance if and when DOJ clearance will be obtained, or as to the conditions or limitations that such DOJ approval may contain or impose.

The approval of any notice or application merely implies satisfaction of regulatory criteria for approval, and does not include review of the particular transaction from the standpoint of the adequacy of the consideration to be received by, or fairness to, shareholders. Regulatory approval does not constitute an endorsement or recommendation of the proposed mergers.

Prosperity and First Bancshares are not aware of any reason why the parties would not be able to obtain the necessary regulatory approvals in a timely manner; however, there can be no assurances when or if the regulatory approvals will be received and, if received, whether they will contain terms, conditions or restrictions not currently contemplated that will be detrimental to or have an adverse impact on Prosperity or its subsidiaries after completion of the First Bancshares merger. Prosperity and First Bancshares believe that the First Bancshares merger should not raise any significant regulatory concerns and that the parties will be able to obtain all required regulatory approvals in a timely manner.

Prosperity and Lone Star are not aware of any reason why the parties would not be able to obtain the necessary regulatory approvals in a timely manner; however, there can be no assurances when or if the regulatory approvals will be received and, if received, whether they will contain terms, conditions or restrictions not currently contemplated that will be detrimental to or have an adverse impact on Prosperity or its subsidiaries after completion of the Lone Star merger. Prosperity and Lone Star believe that the Lone Star merger should not raise any significant regulatory concerns and that the parties will be able to obtain all required regulatory approvals in a timely manner.

If any additional governmental approvals or actions are required, the parties presently intend to seek those approvals or actions. However, the parties cannot assure you that any of these additional approvals or actions will be obtained.

THE REORGANIZATION AGREEMENTS

The following describes certain material provisions of the reorganization agreements, but does not describe all of the terms of the reorganization agreements and may not contain all of the information about the reorganization agreements that is important to you. The following is not intended to provide factual information about the parties or any of their respective subsidiaries or affiliates. The following description of the reorganization agreements is subject to, and qualified in its entirety by reference to, the First Bancshares reorganization agreement, which is attached to this proxy statement/prospectus as Appendix A, and the Lone Star reorganization agreement, which is attached to this proxy statement/prospectus as Appendix B, each of which is incorporated by reference into this proxy statement/prospectus. We urge you to read each of the reorganization agreements carefully and in their entirety, as they are the legal documents governing the respective mergers.

Explanatory Note Regarding the Reorganization Agreements

The reorganization agreements and this summary of terms are included to provide you with information regarding the terms of the reorganization agreements. Factual disclosures about Prosperity, First Bancshares and Lone Star contained in this proxy statement/prospectus or in the public reports of Prosperity filed with the SEC may supplement, update or modify the factual disclosures about Prosperity, First Bancshares and Lone Star contained in the respective reorganization agreements. Each reorganization agreement contains representations and warranties by Prosperity, on the one hand, and by First Bancshares or Lone Star, as applicable, on the other hand. The representations, warranties and covenants made in the reorganization agreements by Prosperity, First Bancshares and Lone Star were qualified and subject to important limitations agreed to by Prosperity, First Bancshares and Lone Star in connection with negotiating the terms of the respective reorganization agreements. In particular, in your review of the representations and warranties contained in the reorganization agreements and described in this summary, it is important to bear in mind that the representations and warranties were negotiated with the principal purpose of establishing circumstances in which a party to the applicable reorganization agreement may have the right not to consummate the applicable merger if the representations and warranties of the other party to that reorganization agreement prove to be untrue due to a change in circumstance or otherwise, and allocating risk between the parties to the applicable reorganization agreement, rather than establishing matters as facts. The representations and warranties also may be subject to a contractual standard of materiality different from that generally applicable to shareholders and reports and documents filed with the SEC and some were qualified by the matters contained in the confidential disclosure schedules that Prosperity and First Bancshares, or Prosperity and Lone Star, as applicable, each delivered in connection with the applicable reorganization agreement and certain documents filed with the SEC. Moreover, information concerning the subject matter of the representations and warranties, which do not purport to be accurate as of the date of this proxy statement/prospectus, may have changed since the date of the reorganization agreements.

For the foregoing reasons, the representations and warranties or any descriptions of those provisions should not be read alone or relied upon as characterizations of the actual state of facts or condition of Prosperity, First Bancshares and Lone Star or any of their respective subsidiaries or affiliates. Instead, such provisions or descriptions should be read only in conjunction with the other information provided elsewhere in this document or incorporated by reference into this proxy statement/prospectus. Please see “Where You Can Find More Information” beginning on page 141. Prosperity will provide additional disclosures in its public reports to the extent it is aware of the existence of any material facts that are required to be disclosed under federal securities laws and that might otherwise contradict the terms and information contained in the reorganization agreements and will update such disclosure as required by federal securities laws.

Structure of the Mergers

The First Bancshares reorganization agreement (a) provides for the merger of First Bancshares with and into Prosperity, with Prosperity as the surviving corporation in the merger, and (b) contemplates that immediately

following the First Bancshares merger, the merger of FirstCapital Bank with and into Prosperity Bank, with Prosperity Bank as the surviving bank.

The Lone Star reorganization agreement (a) provides for the merger of Lone Star with and into Prosperity, with Prosperity as the surviving corporation in the merger, and (b) contemplates that immediately following the Lone Star merger, the merger of Lone Star Bank with and into Prosperity Bank, with Prosperity Bank as the surviving bank.

The Merger Consideration

First Bancshares Merger Consideration

If the First Bancshares merger is completed, all shares of First Bancshares common stock issued and outstanding immediately prior to the First Bancshares effective time will be converted into an aggregate of 3,583,370 shares of Prosperity common stock and $93,422,648 in cash, less any amounts paid with respect to outstanding equity awards, as set forth in the First Bancshares reorganization agreement. Additionally, the aggregate First Bancshares cash consideration will be reduced on a dollar-for-dollar basis if First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is less than $204,000,000 at closing of the First Bancshares merger. Because of the possibility of an adjustment to the First Bancshares cash consideration, you will not know the exact amount of cash you will receive in connection with the First Bancshares merger when you vote on the First Bancshares reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each First Bancshares shareholder will receive.

For illustration purposes only, if the First Bancshares merger occurs and assuming at the closing that (i) there are [ ] shares of First Bancshares common stock issued and outstanding, (ii) there are [ ] unexercised options to purchase shares of First Bancshares common stock with a weighted average exercise price of $[ ], (iii) First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is equal to or greater than $204,000,000, and (iv) the price per share of Prosperity common stock received in the First Bancshares merger is equal to $[ ], which was the closing price per share of Prosperity common stock on [ ], 2023, then holders of First Bancshares common stock will receive [ ] shares of Prosperity common stock with a value of $[ ] (before adjusting for fractional shares) and $[ ] in cash for each share they own, for an aggregate implied value of $[ ] for each share of First Bancshares common stock.

For purposes of determining First Bancshares’ equity capital at closing, the parties have agreed that First Bancshares will deduct or accrue as of the closing of the First Bancshares merger for certain amounts (without duplication), including the after-tax amount of financial advisory, accounting and legal expenses, the after-tax costs to obtain extended reporting period insurance coverage as discussed herein, any amounts required to increase First Bancshares’ allowance for loan losses to the minimum allowance amount required under the First Bancshares reorganization agreement, the estimated after-tax amount of any penalty or liquidated damages associated with the termination of First Bancshares’ data processing agreement, the after-tax amount of any payments to be made under employee-related agreements (other than First Bancshares stock options), the after-tax amount required to fully fund, terminate and liquidate any First Bancshares employee benefit plan, the after-tax amount of any fees, costs and expenses and the estimated after-tax amount related to any required accruals related to certain litigation matters, and the after-tax amount required to pay dividends for one quarter with respect to First Bancshares’ trust preferred securities, among other things.

Lone Star Merger Consideration

Prosperity common stock and $64,053,717 in cash, less any amounts paid with respect to outstanding equity awards, as set forth in the Lone Star reorganization agreement. Additionally, the aggregate Lone Star cash consideration will be reduced on a dollar-for-dollar basis if Lone Star’s equity capital, as calculated under the Lone Star reorganization agreement, is less than $121,088,508 at closing of the Lone Star merger. Because of the possibility of an adjustment to the Lone Star cash consideration, you will not know the exact amount of cash you will receive in connection with the Lone Star merger when you vote on the Lone Star reorganization agreement. Additionally, any exercise of equity awards prior to closing may change the number of shares or amount of cash each Lone Star shareholder will receive.

For purposes of determining Lone Star’s equity capital at closing, the parties have agreed that Lone Star will deduct or accrue as of the closing of the Lone Star merger for certain amounts (without duplication), including the after-tax amount of financial advisory, accounting and legal expenses, the after-tax costs to obtain extended reporting period insurance coverage as discussed herein, any amounts required to increase Lone Star’s allowance for loan losses to the minimum allowance amount required under the Lone Star reorganization agreement, the estimated after-tax amount of any penalty or liquidated damages associated with the termination of Lone Star’s data processing agreement, the after-tax amount of any payments to be made under employee-related agreements (other than Lone Star stock options or stock appreciation rights), the after-tax amount of certain payments to be made to holders of Lone Star stock options, the after-tax amount required to fully fund, terminate and liquidate any Lone Star employee benefit plan, and the after-tax amount of any fees, costs and expenses and the estimated after-tax amount related to any required accruals related to outstanding litigation, among other things. Prosperity and Lone Star also have agreed that if any required regulatory approval requires divestitures in certain markets, Lone Star would accrue one-half of the cost associated with any such divestitures for purposes of its closing equity capital, up to $16 million.

Fractional Shares

Prosperity will not issue any fractional shares of Prosperity common stock in the mergers. Instead, First Bancshares shareholders and Lone Star shareholders who otherwise would have been entitled to a fractional share of Prosperity common stock will receive, in lieu thereof, an amount in cash, rounded up to the nearest whole cent (without interest), determined by multiplying the fraction of a share (rounded to the nearest thousandth when expressed in decimal form) of Prosperity common stock to which such holder would otherwise be entitled by the First Bancshares/Prosperity average price or the Lone Star/Prosperity average price, respectively.

Treatment of Equity Awards

First Bancshares Stock Options

converted into the right to receive a cash payment equal to the difference between the per award share merger consideration (as defined in the First Bancshares reorganization agreement) and the per share exercise price for each share of First Bancshares common stock subject to such First Bancshares stock option. Payments to holders of First Bancshares stock options will reduce the aggregate cash consideration to be paid to First Bancshares shareholders.

Lone Star Stock Options and Stock Appreciation Rights

At the Lone Star effective time, subject to the terms and conditions of the Lone Star reorganization agreement, each option granted by Lone Star to purchase shares of Lone Star common stock and each stock appreciation right under the Lone Star equity compensation plans will fully vest and be cancelled and converted into the right to receive a cash payment equal to the difference between the per award share merger consideration (as defined in the Lone Star reorganization agreement) and the per share exercise price (in the case of stock options) or initial value (in the case of stock appreciation rights) for each share of Lone Star common stock subject to such Lone Star stock option or stock appreciation right. Payments to holders of Lone Star stock options will reduce the aggregate cash consideration to be paid to Lone Star shareholders.

Treatment of Shares of Prosperity Common Stock

Each share of Prosperity common stock outstanding immediately prior to the First Bancshares effective time and the Lone Star effective time will, on and after the applicable effective time, remain issued and outstanding as one share of common stock of Prosperity as the surviving corporation in the First Bancshares merger and the Lone Star merger, respectively.

Effective Time of the Mergers

Each merger will be completed only if all conditions to such merger discussed in this proxy statement/prospectus and set forth in the applicable reorganization agreement are either satisfied or waived (subject to applicable law). See the section entitled “—Conditions to Completion of the Mergers” below.

Each merger will become effective as of the date and time specified in the certificate of merger filed with respect to such merger with the Secretary of State of the State of Texas. We refer to the effective time of the First Bancshares merger as the “First Bancshares effective time” and the effective time of the Lone Star merger as the “Lone Star effective time.” Subject to the receipt of applicable shareholder and regulatory approvals, and the satisfaction or waiver of the other conditions to the applicable parties’ obligations to effect the respective mergers, we anticipate that the mergers will be completed during the first quarter of 2023, although delays could occur. However, we cannot assure you that the necessary shareholder or governmental approvals will be obtained or that the other conditions to completion of the mergers can or will be satisfied or waived.

Exchange Procedures

If you are a holder of First Bancshares common stock or Lone Star common stock, as soon as practicable after the First Bancshares effective time or the Lone Star effective time, as applicable, with the intent to be no later than ten business days after the applicable effective time, Prosperity will use commercially reasonable efforts to cause Computershare Investor Services, Inc., which we refer to as the “exchange agent,” to mail to each record holder of an outstanding certificate or certificates representing shares of First Bancshares common stock or Lone Star common stock, respectively, a form of letter of transmittal and instructions to you for use in surrendering your First Bancshares certificates or Lone Star certificates, respectively.

When you properly surrender your First Bancshares certificates or Lone Star certificates or provide other satisfactory evidence of ownership, and return the applicable letter of transmittal duly executed and completed in accordance with its instructions, the exchange agent will cancel the surrendered stock certificates and deliver to

you a notice specifying, among other things, the number of shares of Prosperity common stock, which will be solely in uncertificated book-entry form credited to the account of the holder of record as established in the Direct Registration System, and cash for fractional shares, if any, to which you are entitled under the First Bancshares reorganization agreement or the Lone Star reorganization agreement, respectively. No stock certificates will be issued with respect to the Prosperity common stock to be issued under the reorganization agreements.

You should not send in your certificates until you receive the applicable letter of transmittal and instructions, which will be mailed as soon as practicable after the First Bancshares effective time or the Lone Star effective time, as applicable.

Until surrendered as described above, (1) each First Bancshares certificate (other than First Bancshares certificates representing cancelled shares) will, from and after the First Bancshares effective time, represent for all purposes only the right to receive the First Bancshares merger consideration without any interest thereon, and (2) each Lone Star certificate (other than Lone Star certificates representing cancelled shares) will, from and after the Lone Star effective time, represent for all purposes only the right to receive the Lone Star merger consideration without any interest thereon.

With respect to any First Bancshares certificate or Lone Star certificate that has been lost, stolen or destroyed, upon making of an affidavit of that fact by the person claiming such First Bancshares certificate or Lone Star certificate to be lost, stolen or destroyed, and, if required by Prosperity or the exchange agent, the posting by such person of a bond as indemnity against any claim that may be made with respect to such First Bancshares certificate or Lone Star certificate, the exchange agent will issue in exchange for such lost, stolen or destroyed First Bancshares certificate or Lone Star certificate the applicable merger consideration deliverable in respect thereof.

After the First Bancshares effective time and the Lone Star effective time, the transfer books of each of First Bancshares and Lone Star, respectively, will be closed and there will be no transfers of the shares of First Bancshares common stock or Lone Star common stock outstanding immediately prior to the First Bancshares effective time and Lone Star effective time, respectively.

Withholding

Prosperity will be entitled to deduct and withhold, or cause the exchange agent to deduct and withhold, from any cash in lieu of fractional shares of Prosperity common stock, cash dividends or distributions payable or any other amount payable under the applicable reorganization agreement to any holder of First Bancshares common stock or equity awards or Lone Star common stock or equity awards, as applicable, such amounts as it is required to deduct and withhold under the Code or any provision of state, local or non-U.S. tax law. To the extent any such amounts are so withheld by Prosperity or the exchange agent, as the case may be, and paid over to the appropriate governmental authority, the withheld amounts will be treated for all purposes of the applicable reorganization agreement as having been paid to the holder of First Bancshares common stock or equity awards or Lone Star common stock or equity awards, as applicable, in respect of which the deduction and withholding was made by Prosperity or the exchange agent, as the case may be.

Conditions to Completion of the Mergers

The respective obligations of each party to consummate the applicable merger and the other transactions contemplated by the applicable reorganization agreement are subject to the satisfaction or waiver at or prior to the effective time of the applicable merger of the following conditions:

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receipt of all required regulatory approvals of transactions contemplated by the applicable reorganization agreement, including the mergers of FirstCapital Bank with and into Prosperity Bank

and Lone Star Bank with and into Prosperity Bank, respectively, in a manner that does not impose any restrictions on the operations of Prosperity or the continuing entity which are reasonably unacceptable to Prosperity;

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approval of the applicable reorganization agreement by the holders of at least two-thirds of the outstanding shares of First Bancshares common stock or Lone Star common stock, as applicable;

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receipt by each party of an opinion of such party’s counsel to the effect that the applicable merger will qualify as a reorganization under Section 368(a) of the Code;

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the registration statement of which this proxy statement/prospectus forms a part having become effective and no stop order suspending its effectiveness being in effect and no proceedings for that purpose being initiated, continuing or threatened by the SEC, and all necessary approvals under state securities laws relating to the issuance or trading of the Prosperity common stock to be issued having been received;

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the shares of Prosperity common stock to be issued pursuant to the applicable merger being authorized for listing on the NYSE;

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the other party’s representations and warranties contained in the applicable reorganization agreement being true and correct in all material respects as of the date of the applicable reorganization agreement and as of the date of the applicable closing, and receipt of a certificate signed by an authorized representative of the other party to that effect;

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the performance or compliance in all material respects by each party with its respective covenants and obligations required by the applicable reorganization agreement to be performed or complied with prior to the closing of the applicable merger and receipt of a certificate executed by an authorized representative of the other party to that effect; and

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the absence of a material adverse change in the assets, properties, deposits, results of operations, earnings, cash flows, business or financial condition of either party to the applicable reorganization agreement or any event that could reasonably be expected to cause or prevents or materially impairs the ability of a party to consummate the applicable merger.

In addition to the conditions listed above, Prosperity’s obligation to complete the applicable merger is subject to the satisfaction of the following conditions by Prosperity:

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each director and certain officers of First Bancshares and FirstCapital Bank and of Lone Star and Lone Star Bank, as applicable, having executed a release agreement;

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with respect to the First Bancshares merger, termination of all outstanding deferred cash incentive agreements by FirstCapital Bank and execution of a termination and release agreement by each such employee;

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with respect to the Lone Star merger, cancellation of all outstanding stock options by Lone Star and execution of a cancellation and release agreement by each holder of a Lone Star stock option;

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certain officers of First Bancshares and/or FirstCapital Bank, with respect to the First Bancshares merger, and Lone Star and/or Lone Star Bank, with respect to the Lone Star merger, each having entered into an employment agreement with Prosperity, which have been executed, and with each such agreement remaining in full force and effect;

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each non-employee director of First Bancshares or FirstCapital Bank, with respect to the First Bancshares merger, and of Lone Star or Lone Star Bank, with respect to the Lone Star merger, having entered into a support (non-competition) agreement with Prosperity, which agreements have been executed, and with each such agreement remaining in full force and effect;

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holders of no more than 5% of the outstanding First Bancshares common stock or Lone Star common stock, as applicable, having demanded or being entitled to receive payment of the fair value of their shares as dissenting shareholders;

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all consents, approvals, waivers and other assurances from all non-governmental third parties identified in the reorganization agreement having been obtained, and Prosperity having received evidence thereof in form and substance satisfactory to it;

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with respect to the Lone Star merger, the allowance for loan losses of Lone Star as of the closing date being equal to at least 1.25% of its total loans, subject to certain adjustments.

Any condition to the completion of the First Bancshares merger or the Lone Star merger, except the required shareholder and regulatory approvals, and the absence of an order or ruling prohibiting the applicable merger, may be waived in writing by the party to the applicable reorganization agreement entitled to the benefit of such condition.

Conduct of Business Pending Effective Time

Except as otherwise expressly permitted or required by the applicable reorganization agreement or as required by applicable law, subject to certain specified exceptions, during the pendency of the applicable reorganization agreement, each of First Bancshares and Lone Star has agreed to and has agreed to cause each of its respective subsidiaries to:

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maintain its corporate existence in good standing;

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use commercially reasonable efforts to maintain the general character of its business and conduct its business in its ordinary and usual manner consistent with past practices;

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use commercially reasonable efforts to preserve its business organization intact; to retain the services of its present employees, officers, directors and agents; to retain its present customers, depositors, suppliers and correspondent banks; and to preserve its goodwill and the goodwill of its suppliers, customers and others having business relationships with it;

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extend credit only in material compliance with lending policies and practices existing on the date of the applicable reorganization agreement;

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promptly give written notice to Prosperity of the following: (a) any material change in its business, operations or prospects, (b) any complaints, investigations or hearings (or communications indicating the same may be contemplated) of any regulatory authority, (c) the institution or threat of any material litigation against First Bancshares or any of its subsidiaries or Lone Star or any of its subsidiaries, as applicable, or (d) the occurrence of an event, the failure of an event to occur or the existence of a circumstance that would reasonably be expected to cause (1) a material breach of a covenant, condition or agreement contained in the applicable reorganization agreement, (2) any representation or warranty of First Bancshares or Lone Star contained in the applicable reorganization agreement to be untrue or inaccurate in any material respect or (3) a material adverse effect (as defined in the applicable reorganization agreement) on Lone Star or Lone Star Bank or on First Bancshares or FirstCapital Bank, as applicable;

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except as required by law or regulation or expressly permitted by the applicable reorganization agreement, take no action which would adversely affect or delay the ability of First Bancshares or Lone Star, as applicable, or Prosperity to obtain any regulatory or other approvals required for the completion of the applicable merger or to perform its obligations and agreements under the applicable reorganization agreement;

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maintain all offices, machinery, equipment, materials, supplies, inventories and properties owned, leased or used by it (whether under its control or the control of others) in good operating repair and condition, ordinary wear and tear excepted;

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timely file all tax returns required to be filed by it and promptly pay all taxes, assessments, governmental charges, duties, penalties, interest and fines that become due and payable, except those being contested in good faith by appropriate proceedings;

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continue to identify, monitor, classify and treat all assets in substantially the same manner as it has in the past and in accordance with applicable law;

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account for all transactions in accordance with GAAP;

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perform all of its material obligations under contracts, leases and documents relating to or affecting its assets, properties and business, except such obligations as it may in good faith reasonably dispute;

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maintain and keep in full force and effect, in all material respects, presently existing insurance coverage and give all notices and present all claims under all insurance policies in due and timely fashion; and

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timely file all reports required to be filed with governmental authorities which shall conform, in all material respects, to applicable law.

Except as otherwise expressly permitted or required by the applicable reorganization agreement or as required by applicable law, subject to certain specified exceptions, during the pendency of the applicable reorganization agreement, without the prior written consent of Prosperity, which consent will not be unreasonably withheld or delayed, First Bancshares and Lone Star will not, and each of First Bancshares and Lone Star will cause each of its respective subsidiaries not to:

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introduce any new material method of management or operation;

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intentionally take any action that would reasonably be anticipated to result in a material adverse effect on First Bancshares or FirstCapital Bank or on Lone Star or Lone Star Bank, as applicable, or prevent or materially delay the ability of the parties to consummate the transactions contemplated by the applicable reorganization agreement;

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take or fail to take any action that would reasonably be expected to cause the representations and warranties of First Bancshares or Lone Star, as applicable, to be inaccurate in any material respect at the applicable closing;

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cause or allow the loss of insurance coverage, unless replaced with coverage which is substantially similar (in amount, scope and insurer) to that in effect as of the date of the applicable reorganization agreement;

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redeem, purchase or otherwise acquire, directly or indirectly, or adjust, split, combine or reclassify, any of its capital stock or other securities;

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except pursuant to existing commitments entered into prior to the date of the applicable reorganization agreement, make or acquire, renew or extend any loans that, (i) with respect to loans to existing customers, increase the aggregate outstanding commitments to any such existing customer by more than $2,000,000 (in the case of First Bancshares) or by more than $1,000,000 (in the case of Lone Star), or (ii) with respect to loans to new customers, result in an aggregate commitment to any such new customer in excess of $2,000,000 (in the case of First Bancshares) or by more than $1,000,000 (in the case of Lone Star), in each case, without first notifying and, if requested by Prosperity within one business day of receipt of such notice, consulting with Prosperity;

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issue or sell or obligate itself to issue or sell any shares of its capital stock or any warrants, rights or options to acquire, or any securities convertible into, any shares of its capital stock;

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grant any stock appreciation rights, stock appreciation units, restricted stock, stock options or other form of equity-based compensation;

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open, close or relocate any branch office, or acquire or sell or agree to acquire or sell, any branch office or any deposit liabilities;

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enter into, amend or terminate certain agreements specified in the applicable reorganization agreement, or any other material agreement, or acquire or dispose of any material amount of assets or liabilities or make any change in any of its leases, except in the ordinary course of business consistent with past practices and safe and sound banking practices;

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except in the ordinary course of business consistent with past practice, grant any severance or termination payment to, or enter into any employment, independent contractor, consulting, noncompetition, retirement, parachute, retention, severance, indemnification or similar agreement or arrangement with, any officer, director, employee or agent of First Bancshares or Lone Star, as applicable, or one of its respective subsidiaries, either individually or as part of a class of similarly situated persons;

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increase in any manner the compensation or benefits, including incentive compensation, of any of its current or former employees, officers, directors, independent contractors or consultants, accelerate the vesting, funding or payment of any compensation or benefit, including incentive compensation, or pay or provide any perquisite such as automobile allowance, club membership or dues or other similar benefits, in each case other than in accordance with past practice or pursuant to policies as in effect as of the date of the applicable reorganization agreement;

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hire or otherwise enter into any employment or independent contractor or consulting agreement or arrangement with any individual whose compensation would exceed $100,000 on an annualized basis;

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terminate the employment of any employee, or service of any independent contractor, of First Bancshares or Lone Star, as applicable, or any of their respective subsidiaries whose annual target compensation opportunity is $100,000 or more (other than a termination of employment or service for cause in the ordinary course of business consistent with past practices);

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adopt or commence participation in any benefit plan of First Bancshares or Lone Star, as applicable, amend or modify any such benefit plan, except as required to maintain the tax qualified status of such plan, or terminate or withdraw from participation in any benefit plan of First Bancshares or Lone Star, as applicable;

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with respect to First Bancshares, (a) declare, pay or set aside for payment any dividend or other distribution (whether in cash, stock or property) in respect of First Bancshares common stock or preferred stock, other than (1) the payment of dividends from FirstCapital Bank to First Bancshares, (2) provided that the First Bancshares effective time is not scheduled to occur on or between the declaration and payment dates, other than the first fiscal quarter of 2023, the declaration and payment of the regular quarterly dividend to the shareholders of First Bancshares in accordance with past practice of no more than $0.05 per share and the regular fourth quarter dividend to the shareholders of First Bancshares of no more than $0.80 per share, (3) with respect to the first fiscal quarter of 2023, any dividend payable by First Bancshares in an amount per share equal to the greater of (i) the product of (x) the per share amount of Prosperity’s first fiscal quarter of 2023 dividend and (y) the per share First Bancshares stock consideration that would be payable for each share of First Bancshares common stock if the First Bancshares closing date would have been the record date for Prosperity’s first fiscal quarter of 2023 dividend and (ii) $0.05, or (4) the payment of dividends on First Bancshares trust securities, or (b) directly or indirectly, purchase, redeem or otherwise acquire any shares of First Bancshares common stock;

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with respect to Lone Star, (a) declare, pay or set aside for payment any dividend or other distribution (whether in cash, stock or property) in respect of Lone Star common stock, other than (1) the payment of dividends from Lone Star Bank to Lone Star or (2) dividends to the shareholders of Lone Star in an amount that, in the good faith reasonable judgment of Lone Star based on consultation with its own tax advisors, is sufficient to satisfy the estimated tax obligations of Lone Star shareholders with respect to net taxable income or gain allocated to such shareholders with respect to any period commencing after June 30, 2022, or (b) directly or indirectly, purchase, redeem or otherwise acquire any shares of Lone

Star common stock, except as required under the Lone Star employee stock ownership plan; provided that Lone Star may use amounts that Lone Star Bank receives in any monetary settlement with respect to certain pre-existing legal proceedings to pay a dividend to its shareholders, subject to certain agreed-upon limits;

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make any change in accounting methods, principles and practices, except as may be required by GAAP or any governmental authority;

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sell, transfer, convey, mortgage, encumber or otherwise dispose of any properties or assets (including other real estate owned) or interest therein, other than the other real estate owned properties under contract for sale as of the date of the applicable reorganization agreement;

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foreclose upon or otherwise acquire any commercial real property having an appraised value of greater than $100,000 prior to receipt and approval by Prosperity of a Phase I environmental review thereof, other than, solely with respect to Lone Star, those properties set forth on a schedule to the Lone Star reorganization agreement;

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increase or decrease the rate of interest paid on deposit accounts, except in a manner and pursuant to policies consistent with First Bancshares’ or Lone Star’s, as applicable, past practices and safe and sound banking practices;

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charge-off any loan or other extension of credit of $100,000 or more prior to review and approval by Prosperity of the amount of such charge-off;

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incur any indebtedness, obligation or liability, whether absolute or contingent, other than the receipt of deposits and trade debt, Federal Home Loan Bank borrowings with maturities of six months or less, sales of certificates of deposit, issuances of commercial paper and entering into repurchase agreements, in each case in the ordinary course of business;

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materially deviate from policies and procedures existing as of the date of the applicable reorganization agreement with respect to (a) classification of assets, (b) the allowance for loan losses and (c) accrual of interest on assets, except as otherwise required by the provisions of the applicable reorganization agreement, applicable law or regulation or any governmental authority;

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amend or change any provision of the certificate of formation or bylaws or other governing documents of First Bancshares or Lone Star, as applicable, or any of their respective subsidiaries;

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make any capital expenditures that would exceed an aggregate of $100,000, except pursuant to commitments made prior to the date of the applicable reorganization agreement;

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discharge or satisfy any lien or pay any obligation or liability, whether absolute or contingent, due or to become due, except in the ordinary course of business and consistent with past practices;

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acquire any capital stock or other equity securities or acquire any equity or ownership interest in or material assets or businesses of any person, including any bank, corporation, partnership or other entity, except (1) through settlement of indebtedness, foreclosure, or the exercise of creditors’ remedies or (2) in a fiduciary capacity, the ownership of which does not expose it to any liability from the business, operations or liabilities of such person;

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merge or consolidate with any other person or restructure, reorganize or completely or partially liquidate or dissolve;

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except with respect to the collection of checks and other negotiable instruments or otherwise in the ordinary course of the business and consistent with past practices, enter into or give any promise, assurance or guarantee of the payment, discharge or fulfillment of any undertaking or promise made by any other third person, firm or corporation;

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sell or knowingly dispose of, or otherwise divest itself of the ownership, possession, custody or control, of any corporate books or records of any nature that, in accordance with past practices, normally are

retained for a period of time after their use, creation or receipt, except at the end of the normal retention period;

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change in any material respect its lending, investment, underwriting, risk and asset liability management, interest rate or fee pricing, hedging and other material banking and operating policies or practices, except as required by law or any governmental body;

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settle any litigation, claim, action or proceeding other than settlements in the ordinary course of business consistent with past practices involving solely money damages not in excess of $50,000 individually or $250,000 in the aggregate that does not involve or create an adverse precedent and that would not impose any material restriction on the business of either party (including the surviving corporation) to the respective reorganization agreements or their respective subsidiaries;

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make any material changes to its securities portfolio from that as of June 30, 2022, through purchases, sales or otherwise (but not redemptions by the issuers of such securities), or the manner in which the portfolio is classified or reported; provided, however, that First Bancshares and FirstCapital Bank, and Lone Star and Lone Star Bank, as applicable, may (A) manage its investment securities in the ordinary course of business consistent with past practice, (B) sell any investment securities after advising Prosperity of the planned sale via e-mail transmission at least two business days prior to such sale and (C) purchase U.S. governmental agency securities, mortgage-backed securities (other than private label mortgage-backed securities) and municipal securities having a maturity date no greater than one year after prior written notice to Prosperity;

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make, change or revoke any material tax election or method of tax accounting, enter into any closing agreement or settle, compromise or abandon any material audit or other proceeding relating to taxes, or file any material amended tax return;

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take any action that could reasonably be expected to prevent the applicable merger from constituting a reorganization within the meaning of Section 368(a) of the Code; or

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agree to do any of the foregoing.

For a complete description of such restrictions on the conduct of the business of First Bancshares and Lone Star, we refer you to the First Bancshares reorganization agreement and the Lone Star reorganization agreement, respectively, which are attached as Appendix A and Appendix B to this proxy statement/prospectus.

No Solicitation

Each of First Bancshares and Lone Star has agreed that neither it, nor any of its subsidiaries, nor any of their respective directors, officers, agents or representatives will directly or indirectly take any action to:

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solicit, initiate, encourage or facilitate the making of any inquiries, or provide any information to, conduct any assessment of or participate in discussions or negotiate with any other party, with respect to any proposal which could reasonably be expected to lead to an acquisition proposal;

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approve, endorse, recommend or enter into any acquisition agreement relating to any acquisition proposal; or

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propose or agree to do any of the foregoing.

If First Bancshares or Lone Star or any of their respective representatives receives an unsolicited bona fide acquisition proposal before the First Bancshares special meeting or Lone Star special meeting, as applicable, that the First Bancshares board of directors or Lone Star board of directors, as applicable, has:

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determined in its good faith judgment (after consultation with its financial advisors and outside legal counsel) that such acquisition proposal constitutes or would reasonably be expected to result in a superior proposal;

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determined in its good faith judgment (after consultation with outside legal counsel) that the failure to take such action would cause it to violate its fiduciary duties under applicable law; and

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obtained from such person or entity an executed confidentiality agreement,

then First Bancshares or Lone Star, as applicable, or their respective representatives may furnish information to and enter into discussions and negotiations with such other party.

Each of First Bancshares and Lone Star has agreed to notify Prosperity orally immediately, and in writing within one business day, after receipt of any unsolicited acquisition proposals or inquiries regarding any acquisition proposals and provide reasonable detail as to the identity of the person making such proposal and the material terms of such acquisition proposal, request or inquiry.

Additional Agreements

In addition to the agreements described above, each party has agreed in the applicable reorganization agreement to take certain other actions, including but not limited to:

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each party has agreed to take all reasonable actions to aid and assist in the completion of the applicable merger and use commercially reasonable best efforts to take or cause to be taken all other actions necessary, proper or advisable to complete the transactions contemplated by the applicable reorganization agreement, including such actions which are necessary, proper or advisable in connection with filing applications with, or obtaining approvals from all regulatory authorities having jurisdiction over the transactions contemplated by the applicable reorganization agreement;

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each party has agreed to give the other party reasonable access to its properties, books and records and to provide additional financial and operating data and other information about its business and properties;

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each party has agreed to hold in confidence documents and information concerning the other in accordance with the terms of a previously executed confidentiality agreement;

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each party has agreed that it will not, and will cause its respective representatives not to, directly or indirectly, before or after the completion of the applicable merger or termination of the applicable reorganization agreement, disclose any confidential information for any reason other than in connection with the regulatory notice and application process;

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each party has agreed that it will not issue or cause the publication of any press release or public announcement with respect to the transactions contemplated by the applicable reorganization agreement without the consent of the other party except as required by applicable law or securities exchange rules or in connection with the regulatory application process;

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First Bancshares has agreed to cooperate with Prosperity to facilitate Prosperity’s assumption of the First Bancshares trust preferred securities;

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each of First Bancshares and Lone Star has agreed, to the extent permitted by law, to provide Prosperity all information concerning First Bancshares and Lone Star, respectively, required for inclusion in this proxy statement/prospectus, or any other application, filing, statement or document to be made or filed in connection with the transactions contemplated by the respective reorganization agreements;

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each of First Bancshares and Lone Star has agreed to deliver or make available to Prosperity all unaudited monthly and quarterly financial statements and all call reports filed by FirstCapital Bank and Lone Star Bank, respectively;

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each of First Bancshares and Lone Star has agreed that it will provide, for a period of at least four years after the effective time of the applicable merger, past acts insurance for no less than the four-year

100

period immediately preceding the effective time of the applicable merger under its (1) current directors’ and officers’ insurance policy (or comparable coverage), and (2) employment practices liability insurance for each director and officer of First Bancshares or Lone Star, respectively, or their respective subsidiaries currently covered under comparable policies held by First Bancshares or Lone Star, respectively, or any of their respective subsidiaries;

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each of First Bancshares and Lone Star has agreed to execute and deliver such instruments and take such actions as Prosperity reasonably requests to cause the amendment or termination of any of the employee benefit plans of First Bancshares and Lone Star, respectively, requested by Prosperity;

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Prosperity has agreed that the employees of First Bancshares and Lone Star, respectively, and their respective subsidiaries who continue their employment after the closing of the applicable merger will be entitled to participate as newly hired employees in the employee benefit plans and programs maintained for employees of Prosperity and Prosperity Bank, such employees will be entitled to credit for prior service with First Bancshares and Lone Star, respectively, and Prosperity will use its reasonable best efforts to facilitate such coverage, including, without limitation, waiving any eligibility waiting periods and pre-existing condition exclusions, to the extent allowed by Prosperity’s plans and applicable law and subject to the provisions set forth in the applicable reorganization agreement;

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each of First Bancshares and Lone Star has agreed to make such accounting entries consistent with GAAP as Prosperity may reasonably request in order to conform the accounting records of First Bancshares and Lone Star, respectively, to the accounting policies and practices of Prosperity, but such adjustments will not affect the calculation of First Bancshares’ or Lone Star’s respective equity capital;

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each of First Bancshares and Lone Star has agreed not to reduce its respective allowance for loan losses to total loans to less than 1.36% and 1.25%, respectively, subject to certain adjustments, and if applicable, to take all action necessary to increase the allowance for loan losses to an amount equal to 1.36% and 1.25%, respectively, of total loans on that date, subject to certain adjustments;

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each of First Bancshares and Lone Star has agreed to use its best efforts to ensure that its current data processing contracts and contracts related to the provision of other electronic banking services will be terminated on a mutually agreeable date after the respective merger is completed;

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First Bancshares has agreed to cause FirstCapital Bank to terminate and fully liquidate each deferred cash incentive agreement prior to the First Bancshares closing and pay the amounts due to the participants;

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each of First Bancshares and Lone Star has agreed to use its commercially reasonable efforts to obtain all required consents, approvals, authorizations or waivers;

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each of First Bancshares and Lone Star has agreed to cause FirstCapital Bank and Lone Star Bank, respectively, to cooperate with Prosperity and Prosperity Bank as necessary in conjunction with all approvals, filings and other steps necessary to cause the completion of the combination of FirstCapital Bank with Prosperity Bank, and Lone Star Bank with Prosperity Bank, respectively, with Prosperity Bank in each case surviving, through merger, purchase and assumption or otherwise after the effective time of the First Bancshares merger and the Lone Star merger, respectively;

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Prosperity has agreed to assume, or cause Prosperity Bank to assume, certain survivor benefit agreements of FirstCapital Bank;

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Prosperity has agreed to file all notices and applications for all regulatory approvals required to be obtained by Prosperity or Prosperity Bank in connection with the applicable reorganization agreement and the transactions contemplated thereby and to provide First Bancshares and Lone Star, as applicable, copies of such filings for which confidential treatment has not been requested;

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Prosperity has agreed to file all documents required to be filed to have the shares of the Prosperity common stock to be issued pursuant to the reorganization agreements included for listing on the NYSE and use its commercially reasonable efforts to effect said listing;

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•

Prosperity has agreed to prepare and file a registration statement with the SEC with respect to the shares of Prosperity common stock to be issued pursuant to the reorganization agreements, and use its commercially reasonable efforts to cause the registration statement to become effective; and

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Prosperity has agreed to indemnify the directors and officers of First Bancshares and FirstCapital Bank, and Lone Star or Lone Star Bank, respectively, as of the First Bancshares effective time and the Lone Star effective time, respectively, and for four years thereafter, against costs or expenses, judgments, fines, losses, claims, damages or liabilities incurred in connection with any claim, action, suit, proceeding or investigation, whether civil, criminal, administrative or investigative, arising out of matters existing or occurring at or before the effective time of the applicable merger, whether asserted or claimed before, at or after the effective time of the applicable merger, arising in whole or in part out of or pertaining to the fact that he or she was acting in his or her capacity as a director or officer of First Bancshares or FirstCapital Bank, or Lone Star or Lone Star Bank, respectively, to the fullest extent that the indemnified party would be entitled under the certificate of formation or bylaws of First Bancshares or Lone Star, respectively, or the similar constituent documents of FirstCapital Bank or Lone Star Bank, respectively, as applicable, as in effect on the date of the applicable reorganization agreement and to the extent permitted by applicable law.

Representations and Warranties

In the First Bancshares reorganization agreement and the Lone Star reorganization agreement, each of First Bancshares and Lone Star, respectively, has made customary representations and warranties to Prosperity, and Prosperity has made customary representations and warranties to each of First Bancshares and Lone Star, respectively, relating to their respective businesses, including the following:

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corporate organization and existence;

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authority and power to execute the applicable reorganization agreement and to complete the transactions contemplated by the applicable reorganization agreement;

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the absence of conflicts between the execution of the applicable reorganization agreement and completion of the transactions contemplated by the applicable reorganization agreement and certain other agreements;

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capitalization;

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the accuracy of their financial statements and reports;

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the ability to receive requisite regulatory approvals;

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compliance with applicable laws and regulatory filings; and

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the absence of certain changes and events.

Each of First Bancshares and Lone Star, respectively, also has made additional representations and warranties to Prosperity with respect to (among other things):

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its investments;

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its loan portfolio and reserve for loan losses;

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the existence of certain loan agreements and related matters;

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its fiduciary responsibilities;

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its real property and leases;

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its personal property;

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its compliance with environmental laws;

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pending or threatened litigation and other proceedings;

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compliance with tax laws, payment of taxes and filing of tax returns;

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the existence of certain contracts and commitments;

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its fidelity bonds and insurance coverage;

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actions taken by regulatory authorities;

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employment relations;

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compensation and benefit plans;

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its deferred compensation agreements;

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its brokers’, finders’ and financial advisors’ fees;

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its accounting controls;

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the absence of derivative contracts;

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its deposit accounts;

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its intellectual property rights;

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its shareholders list;

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its status concerning SEC filings and registration of shares;

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dissenting shareholders;

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anti-takeover laws;

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compliance with the Community Reinvestment Act; and

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its receipt of a fairness opinion.

First Bancshares also has made additional representations and warranties to Prosperity with respect to the outstanding trust preferred securities issued by its subsidiary trust.

Prosperity has also made additional representations and warranties to First Bancshares and Lone Star, respectively, with respect to (among other things) its compliance with its SEC reporting obligations and the accuracy of such reports.

Termination of the Reorganization Agreements

Prosperity and Lone Star can mutually agree at any time to terminate the Lone Star reorganization agreement without completing the Lone Star merger, and Prosperity and First Bancshares can mutually agree at any time to terminate the First Bancshares reorganization agreement without completing the First Bancshares merger. In addition, either Prosperity, on the one hand, or First Bancshares or Lone Star, respectively, on the other, may decide, without the consent of the other, to terminate the applicable reorganization agreement if:

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any of the transactions contemplated by the applicable reorganization agreement are not approved by the appropriate regulatory authorities or the applications or notices are suggested or recommended to be withdrawn by any regulatory authorities;

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in the case of the First Bancshares reorganization agreement, the First Bancshares merger has not been completed by May 8, 2023 (unless one or more of the regulatory approvals has not been received on or

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before May 8, 2023, in which case this deadline will be extended to July 7, 2023), and in the case of the Lone Star reorganization agreement, the Lone Star merger has not been completed by April 8, 2023 (unless one or more of the regulatory approvals has not been received on or before April 8, 2023, in which case this deadline will be extended to June 7, 2023), or in each case, such later date approved in writing by the boards of directors of Prosperity and First Bancshares or Lone Star, as applicable, unless the failure to complete the applicable merger by that time is due to a violation of the applicable reorganization agreement by the party that seeks to terminate such reorganization agreement;

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First Bancshares or Lone Star may terminate its reorganization agreement, without the consent of Prosperity, if the board of directors of First Bancshares or Lone Star, as applicable, receives an unsolicited, bona fide alternative “acquisition proposal” (as defined in each reorganization agreement) and, under certain terms and conditions, determines that it is a superior proposal to that of such reorganization agreement and that the failure to accept such proposal would cause the First Bancshares board of directors or Lone Star board of directors, as applicable, to violate its fiduciary duties under applicable law; but First Bancshares or Lone Star, as applicable, must notify Prosperity of the superior proposal at least five business days before terminating the applicable reorganization agreement, during which time Prosperity has the right to adjust the terms and conditions of the applicable reorganization agreement so that the superior proposal no longer constitutes a superior proposal.

Prosperity may also terminate the applicable reorganization agreement if First Bancshares or Lone Star, as applicable, has materially breached its non-solicitation obligations contained in the applicable reorganization agreement in a manner adverse to Prosperity, the board of First Bancshares or Lone Star, as applicable, resolves to accept a competing acquisition proposal or the board of First Bancshares or Lone Star, as applicable, changes its recommendation regarding the applicable merger

Termination Fees and Effect of Termination

If the First Bancshares reorganization agreement or the Lone Star reorganization agreement, as applicable, is terminated by:

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Prosperity because the First Bancshares board of directors or Lone Star board of directors, as applicable, resolves to accept another acquisition proposal;

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If either Prosperity or First Bancshares terminates the First Bancshares reorganization agreement and:

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without regard to timing, First Bancshares’ shareholders have not approved the First Bancshares reorganization agreement and an acquisition proposal exists at the time of termination,

If either Prosperity or Lone Star terminates the Lone Star reorganization agreement and:

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without regard to timing, Lone Star’s shareholders have not approved the Lone Star reorganization agreement and an acquisition proposal exists at the time of termination,

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without regard to timing, First Bancshares’ shareholders have not approved the First Bancshares reorganization agreement and an acquisition proposal exists at the time of termination,

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•

without regard to timing, Lone Star’s shareholders have not approved the Lone Star reorganization agreement and an acquisition proposal exists at the time of termination,

If either reorganization agreement is terminated or abandoned, it will become void and have no further force or effect and there will be no liability on the part of any party to such agreement for any matters addressed in such agreement or other claim relating to such agreement and the transactions contemplated thereby, except that (a) designated provisions of such reorganization agreement will survive the termination, including, but not limited to, those relating to payment of fees and expenses and the confidential treatment of information and (b) the termination of such agreement will not relieve a party of any liability for a breach by it occurring prior to such termination.

Expenses and Fees

Each party will bear and pay all direct costs and expenses incurred by it or on its behalf in connection with the transactions contemplated by the reorganization agreements.

Amendment or Waiver

Prosperity and First Bancshares or Lone Star, as applicable, may amend the applicable reorganization agreement and each party to such reorganization agreement may waive its right to require the other party to adhere to any term or condition of the reorganization agreement. However, the terms of the applicable reorganization agreement may not be amended after the approval of the First Bancshares shareholders and the Lone Star shareholders, as applicable, to change the form or decrease of the amount of the merger consideration, without the further approval by such shareholders.

Director Support Agreements

First Bancshares Director Support Agreements

The non-employee directors of First Bancshares and the non-employee directors of FirstCapital Bank each entered into a director support agreement with Prosperity, First Bancshares and FirstCapital Bank, in connection with Prosperity’s and First Bancshares’ entry into the First Bancshares reorganization agreement, which we refer to as the “First Bancshares director support agreements.” Pursuant to the First Bancshares director support agreements, the First Bancshares non-employee directors have agreed, among other things, and subject to certain exceptions, not to disclose or use confidential information of First Bancshares or Prosperity, and, with respect to certain of the non-employee directors, from and after the First Bancshares effective time for a period of two years, not to solicit customers of First Bancshares or Prosperity on behalf of a third party, not to solicit certain First Bancshares or Prosperity employees and not to compete with Prosperity. The First Bancshares director support agreements become effective upon the First Bancshares effective time; provided that if the First Bancshares reorganization agreement is terminated, the director support agreements will not become effective.

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The foregoing summary of the First Bancshares director support agreements is not complete and is qualified in its entirety by reference to the complete text of the form of such agreements, which is attached to this proxy statement/prospectus as Appendix C and is incorporated by reference into this proxy statement/prospectus.

Lone Star Director Support Agreements

The non-employee directors of Lone Star and the non-employee directors of Lone Star Bank each entered into a director support agreement with Prosperity, Lone Star and Lone Star Bank, in connection with Prosperity’s and Lone Star’s entry into the Lone Star reorganization agreement, which we refer to as the “Lone Star director support agreements.” Pursuant to the Lone Star director support agreements, the Lone Star non-employee directors have agreed, among other things, and subject to certain exceptions, not to disclose or use confidential information of Lone Star or Prosperity, and from and after the Lone Star effective time for a period of two years, not to solicit customers of Lone Star or Prosperity on behalf of a third party, not to solicit certain Lone Star or Prosperity employees and, with respect to certain of the non-employee directors, not to compete with Prosperity. The Lone Star director support agreements become effective upon the Lone Star effective time; provided that if the Lone Star reorganization agreement is terminated, the Lone Star director support agreements will not become effective.

The foregoing summary of the Lone Star director support agreements is not complete and is qualified in its entirety by reference to the complete text of the form of such agreements, which is attached to this proxy statement/prospectus as Appendix D and is incorporated by reference into this proxy statement/prospectus.

Voting Agreements

Each of the directors of First Bancshares and certain executive officers of First Bancshares, as well as each of the directors of Lone Star and certain executive officers and shareholders of Lone Star, in each case in their capacities as individuals, have separately entered into a First Bancshares voting agreement or Lone Star voting agreement, respectively, in which they have agreed to vote (or cause to be voted), in person or by proxy, or deliver (or cause to be delivered) a written consent covering, all covered shares as to which they control the right to vote, subject to certain exceptions, (1) in favor of the adoption and approval of the applicable reorganization agreement and the consummation of the transactions contemplated thereby, including the applicable merger, (2) against any acquisition proposal or other proposal made in opposition to or that is otherwise in competition or inconsistent with the transactions contemplated by the applicable reorganization agreement, (3) against any agreement, amendment of any agreement or organizational document inconsistent with the applicable voting agreement or the applicable reorganization agreement and (4) against any action, agreement, transaction or proposal that would reasonably be expected to result in a breach of any representation, warranty, covenant, agreement or other obligation of First Bancshares or Lone Star, respectively, under such reorganization agreement or that would reasonably be expected to prevent, impede or delay the consummation of the transactions contemplated by the applicable reorganization agreement. In addition, the First Bancshares voting agreements and Lone Star voting agreements provide that such shareholders will not sell or transfer any of their shares of First Bancshares common stock or Lone Star common stock, respectively, of which they are a record owner, subject to certain exceptions, until the earlier of the receipt of the First Bancshares shareholder approval or Lone Star shareholder approval, respectively, or the date on which the applicable reorganization agreement is terminated in accordance with its terms, or, in the case of voting agreements with certain of the First Bancshares non-employee directors, one year after the date of the First Bancshares voting agreements or the date of any amendment to the First Bancshares reorganization agreement in a manner material and adverse to such directors.

The First Bancshares voting agreements and Lone Star voting agreements will remain in effect until the earlier to occur of the closing of the respective merger and the date of termination of the applicable reorganization agreement in accordance with its terms.

As of the First Bancshares record date and Lone Star record date, shares constituting approximately [ ]% of the First Bancshares common stock entitled to vote at the First Bancshares special meeting and approximately

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[ ]% of the Lone Star common stock entitled to vote at the Lone Star special meeting are subject to First Bancshares voting agreements or Lone Star voting agreements, respectively.

The foregoing description of the First Bancshares voting agreements and the Lone Star voting agreements is subject to, and qualified in its entirety by reference to, the First Bancshares voting agreements and Lone Star voting agreements, respectively, forms of which are attached to this proxy statement/prospectus as Appendix E and Appendix F, respectively, and are incorporated by reference into this proxy statement/prospectus.

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ACCOUNTING TREATMENT

The mergers will be accounted for under the acquisition method of accounting under accounting principles generally accepted in the United States of America. Under this method, First Bancshares’ and Lone Star’s respective assets and liabilities as of the date of the applicable merger will be recorded at their respective fair values. Any difference between the purchase price for First Bancshares or Lone Star, as applicable, and the fair value of the identifiable net assets acquired (including intangibles) will be recorded as goodwill. In accordance with ASC Topic 805, Business Combinations, the goodwill resulting from each merger will not be amortized to expense, but instead will be reviewed for impairment at least annually and to the extent goodwill is impaired, its carrying value will be written down to its implied fair value and a charge will be made to earnings. Core deposit and other intangibles with definite useful lives recorded by Prosperity in connection with the mergers will be amortized to expense in accordance with such rules. The consolidated financial statements of Prosperity issued after the mergers will reflect the results attributable to the acquired operations of First Bancshares and Lone Star beginning on the date of completion of the applicable merger.

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MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE MERGERS

The following discussion describes the material U.S. federal income tax consequences of the First Bancshares merger and the Lone Star merger to “U.S. holders” (as defined below) of First Bancshares common stock or Lone Star common stock, respectively, that exchange their shares of First Bancshares common stock or Lone Star common stock, respectively, for shares of Prosperity common stock and cash in either the First Bancshares merger or the Lone Star merger, respectively. The following discussion is based upon the Code, U.S. Treasury regulations promulgated thereunder and judicial and administrative authorities, rulings and decisions, all as in effect as of the date of this proxy statement/prospectus. These authorities may change, possibly with retroactive effect, and any such change could affect the accuracy of the statements and conclusions set forth in this discussion. This discussion does not address any tax consequences arising under the laws of any state, local or foreign jurisdiction, or under any U.S. federal laws other than those pertaining to the income tax, including without limitation, under the federal estate, gift or alternative minimum tax, the unearned income Medicare contribution tax pursuant to the Health Care and Education Reconciliation Act of 2010, any withholding considerations under the Foreign Account Tax Compliance Act of 2010 (including the U.S. Treasury Regulations issued thereunder and intergovernmental agreements entered into pursuant thereto or in connection therewith) or, except as expressly discussed below, any tax reporting requirements.

The following discussion applies only to U.S. holders who hold such shares as capital assets within the meaning of Section 1221 of the Code (generally, property held for investment). Further, this discussion does not purport to consider all aspects of U.S. federal income taxation that might be relevant to U.S. holders in light of their particular circumstances and does not apply to U.S. holders subject to special treatment under the U.S. federal income tax laws (such as, for example, dealers or brokers in securities, commodities or foreign currencies, traders in securities that elect to apply a mark-to-market method of accounting, banks and certain other financial institutions, insurance companies, mutual funds, tax-exempt organizations, holders subject to the alternative minimum tax provisions of the Code, partnerships, S corporations or other pass-through entities or investors therein, regulated investment companies, real estate investment trusts, U.S. expatriates, holders who exercise dissenter’s rights, holders whose functional currency is not the U.S. dollar, holders who hold First Bancshares common stock or Lone Star common stock as part of a hedge, straddle, constructive sale or conversion transaction or other integrated investment, retirement plans, individual retirement accounts, or other tax-deferred accounts, holders who acquired First Bancshares common stock or Lone Star common stock, as applicable, pursuant to the exercise of employee stock options, through a tax qualified retirement plan or otherwise as compensation or holders who actually or constructively own more than 5% of First Bancshares common stock or Lone Star common stock, as applicable).

For purposes of this discussion, the term “U.S. holder” means a beneficial owner of First Bancshares common stock or Lone Star common stock, as applicable, that is for U.S. federal income tax purposes (i) an individual citizen or resident of the United States, (ii) a corporation, or entity treated as a corporation for U.S. federal income tax purposes, organized in or under the laws of the United States or any state thereof or the District of Columbia, (iii) a trust if (A) a court within the United States is able to exercise primary supervision over the administration of the trust and one or more U.S. persons have the authority to control all substantial decisions of the trust or (B) such trust has a valid election in effect to be treated as a U.S. person for U.S. federal income tax purposes or (iv) an estate, the income of which is subject to U.S. federal income tax, regardless of its source.

If an entity or arrangement treated as a partnership for U.S. federal income tax purposes holds First Bancshares common stock or Lone Star common stock, as applicable, the tax treatment of a partner in such partnership generally will depend on the status of the partner and the activities of the partnership. Any entity treated as a partnership for U.S. federal income tax purposes that holds First Bancshares common stock or Lone Star common stock, and any partners in such partnership, should consult their own tax advisors regarding the tax consequences of the applicable merger to their specific circumstances.

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None of the opinions described below will be binding on the Internal Revenue Service (the “IRS”), or any court. None of Prosperity, First Bancshares or Lone Star have sought or will seek any ruling from the IRS regarding any matters relating to the mergers, and as a result, there can be no assurance that the IRS will not assert, or that a court would not sustain, a position contrary to any of the conclusions set forth below. In addition, if any of the representations or assumptions upon which those opinions are based are inconsistent with the actual facts, this discussion of the material U.S. federal income tax consequences of the mergers could be inaccurate. Determining the actual tax consequences of the First Bancshares merger or the Lone Star merger, as applicable, to an individual holder may be complex and will depend on such holder’s specific situation. Each holder should consult his, her or its own tax advisor as to the specific tax consequences of the applicable merger in such holder’s particular circumstances, including the applicability and effect of the alternative minimum tax and any state, local, foreign and other tax laws and of changes in those laws.

Tax Consequences of the Mergers Generally

In connection with the filing with the SEC of the registration statement on Form S-4 of which this proxy statement/prospectus is a part, Bracewell LLP has rendered its tax opinion to Prosperity and Fenimore Kay Harrison LLP has rendered its tax opinion to First Bancshares, addressing the U.S. federal income tax consequences of the First Bancshares merger as described below. Similarly, in connection with the filing with the SEC of the registration statement on Form S-4 of which this proxy statement/prospectus is a part, Bracewell LLP has rendered its tax opinion to Prosperity and Fenimore Kay Harrison LLP has rendered its tax opinion to Lone Star, addressing the U.S. federal income tax consequences of the Lone Star merger as described below. In addition, it is a condition to the obligation of each of Prosperity and First Bancshares to complete the First Bancshares merger that each of Prosperity and First Bancshares receive an opinion from Bracewell LLP and Fenimore Kay Harrison LLP, respectively, dated as of the closing date of the First Bancshares merger, to the effect that the First Bancshares merger will qualify as a “reorganization” within the meaning of Section 368(a) of the Code. Similarly, it is a condition to the obligation of each of Prosperity and Lone Star to complete the Lone Star merger that each of Prosperity and Lone Star receive an opinion from Bracewell LLP and Fenimore Kay Harrison LLP, respectively, dated as of the closing date of the Lone Star merger, to the effect that the Lone Star merger will qualify as a “reorganization” within the meaning of Section 368(a) of the Code. These opinions are and will be subject to customary qualifications and assumptions, including assumptions regarding the absence of changes in existing facts and the completion of the mergers strictly in accordance with the respective reorganization agreements and the registration statement. In rendering their tax opinions and approving this description of the U.S. federal income tax consequences of the respective mergers, each counsel relied, and will rely, upon representations and covenants, including those contained in certificates of officers of Prosperity, First Bancshares and Lone Star, as applicable, reasonably satisfactory in form and substance to each such counsel, and will assume that such representations are true, correct and complete without regard to any knowledge limitation, and that the parties will comply with such covenants. If any of these assumptions or representations are inaccurate in any way, or any of the covenants are not complied with, such opinions and this description could be inaccurate. The opinions and this description represent each counsel’s best legal judgment, but have no binding effect or official status of any kind, and no assurance can be given that contrary positions will not be taken by the IRS or a court considering the issues. In addition, none of Prosperity, First Bancshares or Lone Star has requested or intends to request a ruling from the IRS as to the U.S. federal income tax consequences of the First Bancshares merger or the Lone Star merger, as applicable. Accordingly, there can be no assurances that the IRS will not assert, or that a court will not sustain, a position contrary to any of the tax consequences set forth below or any of the tax consequences described in the tax opinions. The following discussion assumes that the First Bancshares merger and the Lone Star merger will be consummated as described in the applicable reorganization agreement and this proxy statement/prospectus and that none of Prosperity, First Bancshares or Lone Star, as applicable, will waive the closing opinion condition described above in this paragraph.

Tax Consequences to Prosperity, First Bancshares and Lone Star

With respect to the First Bancshares merger and on the basis that the First Bancshares merger qualifies as a “reorganization” within the meaning of Section 368(a) of the Code, each of Prosperity and First Bancshares will

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be considered a “party to a reorganization” within the meaning of Section 368(b) of the Code, and no gain or loss will be recognized by Prosperity or First Bancshares for U.S. federal income tax purposes as a result of the First Bancshares merger. With respect to the Lone Star merger and on the basis that the Lone Star merger qualifies as a “reorganization” within the meaning of Section 368(a) of the Code, each of Prosperity and Lone Star will be considered a “party to a reorganization” within the meaning of Section 368(b) of the Code, and no gain or loss will be recognized by Prosperity or Lone Star for U.S. federal income tax purposes as a result of the Lone Star merger.

U.S. Holders—Treatment of Merger Consideration

On the basis that each merger qualifies as a “reorganization” within the meaning of Section 368(a) of the Code, upon exchanging its First Bancshares common stock or Lone Star common stock, as applicable, for Prosperity common stock and cash, a U.S. holder may recognize gain (in the manner described immediately herein), but will not be permitted to recognize loss, on the difference between such holder’s adjusted tax basis in the First Bancshares common stock or Lone Star common stock, as applicable, surrendered and the sum of the fair market value of the shares of Prosperity common stock and the amount of cash received (other than cash received in lieu of a fractional share of Prosperity common stock). Any gain generally will be recognized in an amount equal to the lesser of (i) the sum of the amount of cash (other than cash received in lieu of a fractional share of Prosperity common stock) and the fair market value of the Prosperity common stock received, minus the adjusted tax basis of the First Bancshares shares or Lone Star shares surrendered in exchange therefor, and (ii) the amount of cash received by the U.S. holder (other than cash received in lieu of a fractional share of Prosperity common stock). Except to the extent any cash received is treated as a dividend as discussed below, any recognized gain generally will be capital gain and will be long-term capital gain if, as of the effective date of the merger, the U.S. holder’s holding period with respect to the First Bancshares shares or Lone Star shares surrendered exceeds one year.

In general, in order for any gain recognized as described above to be treated as capital gain, it must not have the effect of the distribution of a dividend under the tests described in Section 302 of the Code. Otherwise, such gain will be treated as dividend income to the extent of such U.S. holder’s ratable share of Prosperity’s accumulated earnings and profits (as calculated for U.S. federal income tax purposes). Under these tests, the cash will not be treated as a dividend if the holder experiences a “meaningful reduction” in the equity of Prosperity, tested as if the U.S. holder received solely shares of Prosperity common stock in the applicable merger and then had a portion of such shares redeemed for the cash consideration. Depending on a U.S. holder’s particular circumstances, even a small reduction in stock ownership interest may satisfy this test. In particular, based on a published ruling of the IRS, any reduction in the percentage interest of a stockholder whose relative stock interest in a publicly held corporation is minimal (e.g., an interest of less than 1%) and who exercises no control over corporate affairs should constitute a “meaningful reduction.” To the extent that U.S. holders that are corporations might be treated as not having a meaningful reduction, in particular because of the application of certain constructive ownership rules, it is recommended that such holders consult their own tax advisors regarding the potential applicability of the “extraordinary dividend” provisions of the Code.

The aggregate tax basis of the Prosperity common stock received by a U.S. holder that exchanges its First Bancshares common stock or Lone Star common stock, as applicable, for a combination of Prosperity common stock and cash as a result of the First Bancshares merger or Lone Star merger (including any fractional share deemed received and redeemed for cash as described below), respectively, will be the same as the aggregate adjusted tax basis in the First Bancshares shares or Lone Star shares surrendered in exchange therefor, reduced by the amount of cash received on the exchange (excluding cash received in lieu of a fractional share of Prosperity common stock) plus the amount of any gain or dividend income recognized upon the exchange (excluding any gain recognized as a result of any cash received in lieu of a fractional share of Prosperity common stock). A U.S. holder’s holding period for the Prosperity common stock received in the applicable merger (including any fractional share deemed received and redeemed for cash as described below) will include the holding period of the First Bancshares shares or Lone Star shares surrendered. In general, the Prosperity common

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stock received by a U.S. holder that acquired different blocks of First Bancshares common stock or Lone Star common stock at different times or at different prices generally will be allocated pro rata to each block of First Bancshares common stock or Lone Star common stock, and the basis and holding period of each block of Prosperity common stock received will be determined on a block-for-block basis by reference to the blocks of First Bancshares common stock or Lone Star common stock exchanged therefor. We recommend that U.S. holders consult their own tax advisors regarding the manner in which cash and Prosperity common stock should be allocated among their shares of First Bancshares common stock or Lone Star common stock and the manner in which the above rules would apply in their particular circumstance.

Cash In Lieu of Fractional Shares

If a U.S. holder receives cash instead of a fractional share of Prosperity common stock, the U.S. holder will be treated as having received such fractional share of Prosperity common stock pursuant to the applicable merger and then as having received cash in exchange for such fractional share of Prosperity common stock. As a result, the U.S. holder generally will recognize gain or loss equal to the difference between the amount of cash received and the holder’s basis in its fractional share of Prosperity common stock as set forth above. Such gain or loss generally will be capital gain or loss (subject to the rules above regarding possible dividend treatment) and will be long-term capital gain or loss if, as of the effective date of the applicable merger, the holding period for such fractional share (including the holding period of shares of First Bancshares common stock or Lone Star common stock surrendered in exchange therefor) exceeds one year. Long-term capital gains of certain U.S. holders, including individuals, generally are eligible for a reduced rate of taxation. The deductibility of capital losses is subject to limitations.

Information Reporting and Backup Withholding

Under certain circumstances, non-corporate U.S. holders may be subject to information reporting and backup withholding on the receipt of any cash payments. A U.S. holder generally will not be subject to backup withholding, however, if such holder (i) furnishes a correct taxpayer identification number, certifying that such holder is not subject to backup withholding and otherwise complies with all the applicable requirements of the backup withholding rules; or (ii) provides proof that it otherwise is exempt from backup withholding. Any amounts withheld under the backup withholding rules are not an additional tax and generally will be allowed as a refund or credit against the U.S. holder’s U.S. federal income tax liability, provided the U.S. holder timely furnishes the required information to the IRS.

Certain Reporting Requirements

If you are a U.S. holder who receives Prosperity common stock as a result of the First Bancshares merger or Lone Star merger, as applicable, you will be required to retain permanent records and make such records available to any authorized IRS officers and employees. The records should include the number of shares of First Bancshares common stock or Lone Star common stock, as applicable, exchanged, the number of shares of Prosperity common stock received, the fair market value and tax basis in the shares of First Bancshares common stock or Lone Star common stock, as applicable, exchanged and your tax basis in the shares of Prosperity common stock received.

If you are a U.S. holder that receives Prosperity common stock in the First Bancshares merger or the Lone Star merger and you are considered a “significant holder,” you would be required (1) to file a statement with your U.S. federal income tax return in accordance with Section 1.368-3 of the U.S. Treasury Regulations providing certain facts pertinent to the applicable merger, including your tax basis in, and the fair market value of, the First Bancshares common stock or Lone Star common stock, as applicable, you surrendered in the applicable merger (determined immediately before such merger), the names and employer identification numbers of First Bancshares or Lone Star, as applicable, and Prosperity and the date of the applicable merger and (2) to retain

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permanent records of these facts relating to the applicable merger. A “significant holder” is any First Bancshares shareholder or Lone Star shareholder, as applicable, that, immediately before the applicable merger, (1) owned at least 1% (by vote or value) of the outstanding shares of First Bancshares common stock or Lone Star common stock, as applicable, or (2) owned First Bancshares or Lone Star, as applicable, securities with a tax basis of $1.0 million or more.

This discussion of certain material U.S. federal income tax consequences is not intended to be, and should not be construed as, tax advice. It is not a complete analysis or discussion of all potential tax consequences of the First Bancshares merger or the Lone Star merger. Holders of First Bancshares common stock or Lone Star common stock are urged to consult their own tax advisors with respect to the application of U.S. federal income tax laws to their particular situations as well as any tax consequences arising under the U.S. federal estate or gift tax rules, or under the laws of any state, local, foreign or other taxing jurisdiction or under any applicable tax treaty or with respect to the effect of possible changes in any of those laws after the date of this proxy statement/prospectus.

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BUSINESS OF FIRST BANCSHARES

General

First Bancshares is a Texas corporation and a bank holding company registered under the Bank Holding Company Act for FirstCapital Bank. First Bancshares was incorporated in February 2002 for the purpose of serving as a bank holding company for FirstCapital Bank. First Bancshares does not, as an entity, engage in separate business activities of a material nature apart from the activities it performs for its wholly owned banking subsidiary, FirstCapital Bank. Its primary activities are to provide assistance in the management and coordination of FirstCapital Bank’s financial resources. First Bancshares has no significant assets other than all of the outstanding common stock of FirstCapital Bank. First Bancshares derives its revenues primarily from the operations of FirstCapital Bank in the form of dividends received from FirstCapital Bank. As a bank holding company, First Bancshares is subject to the supervision and regulation of the Federal Reserve. First Bancshares does not file reports with the SEC. First Bancshares does, however, voluntarily provide annual reports, including audited financial statements, to its shareholders.

FirstCapital Bank is a national banking association that was chartered in November 1998 and is subject to the supervision and regulation of the Office of the Comptroller of the Currency, or the “OCC.” FirstCapital Bank is a full-service commercial bank, providing financial services to customers primarily located in the Texas market areas of Amarillo, Byers, Burkburnett, Dallas, Fredericksburg, Henrietta, Horseshoe Bay, Lubbock, Marble Falls, Midland, and Wichita Falls.

As of September 30, 2022, First Bancshares had, on a consolidated basis, total assets of approximately $2.2 billion, gross loans of approximately $1.6 billion, total deposits of approximately $1.8 billion, and total shareholders’ equity of approximately $276.7 million.

Products and Services

FirstCapital Bank is a community-oriented, full service financial institution, which emphasizes personal service and contact. FirstCapital Bank meets its commercial and retail customers’ banking needs with a diversified range of financial services. FirstCapital Bank offers personal and business checking accounts, interest-bearing checking accounts, savings accounts, and various types of certificates of deposit. FirstCapital Bank also offers installment loans, working capital loans, real estate loans, construction loans, residential loans, jumbo loans, commercial and home equity lines of credit, boat and auto loans, and credit cards. In addition, FirstCapital Bank provides services online and through a mobile platform such as mobile deposit, person-to-person payments, credit and debit cards as well as a host of other traditional banking services. FirstCapital Bank offers its services through a variety of channels to meet the needs of its customers including in-person through full service branches, automated teller machines, via telephone, online and mobile platforms.

Employees

As of September 30, 2022, FirstCapital had 257 full-time (or full-time equivalent) employees, none of whom is covered by a collective bargaining agreement.

Properties

The main office of First Bancshares and FirstCapital Bank is located at 310 West Wall Street, Midland, Texas 79701. FirstCapital Bank also operates two additional branch offices in Midland, Texas, two branch offices in Amarillo, Texas, two branch offices in Lubbock, Texas, two branch offices in Wichita Falls, Texas, and a branch office in each of Burkburnett, Byers, Dallas, Fredericksburg, Henrietta, Horseshoe Bay, and Marble Falls, Texas.

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Legal Proceedings

There are no threatened or pending legal proceedings against First Bancshares or FirstCapital Bank which, if determined adversely, would, in the opinion of management, have a material adverse effect on First Bancshares’ business, financial condition, results of operations, cash flows or prospects.

Competition

FirstCapital Bank operates an aggregate of 16 full-service banking offices among the Texas banking markets of Amarillo, Dallas, Fredericksburg, Lubbock, Marble Falls (which includes Horseshoe Bay, Texas), Odessa-Midland, and Wichita Falls (which includes the Texas cities of Buyers, Burkburnett and Henrietta). The Texas banking markets are each a highly competitive environment for commercial banking. The following table lists FirstCapital Bank’s deposit market share, as reported by the Federal Reserve’s CASSIDI as of June 30, 2022, for each banking market in which FirstCapital Bank has a branch.


Market Area	Market Rank		No. of Institutions in Market		Deposits In Market		Market Share
					(in millions)
Amarillo, Texas		11		23	$	3,289		1.06	%
Dallas, Texas		110		143	$	1,912		0.1	%
Fredericksburg, Texas		10		12	$	1,862		2.60	%
Lubbock, Texas		14		28	$	928		1.17	%
Marble Falls, Texas		7		17	$	1,067		5.02	%
Odessa-Midland, Texas		7		19	$	924		6.78	%
Wichita Falls, Texas		4		14	$	1,557		11.50	%

First Bancshares experiences competition in its markets from many other financial institutions, including when attracting and retaining savings deposits and in lending funds. The primary factors First Bancshares encounters in competing for savings deposits are convenient office locations and rates offered. Direct competition for savings deposits comes from other commercial bank and thrift institutions, credit unions, money market mutual funds and issuers of corporate and government securities which may offer more attractive rates than insured depository institutions are willing to pay. The primary factors First Bancshares encounters in competing for loans include, among others, interest rate and loan origination fees and the range of services offered. Competition for origination of real estate loans comes from other commercial banks, thrift institutions, mortgage bankers, mortgage brokers and insurance companies. Banks and other financial institutions with which First Bancshares competes may have capital resources and legal loan limits substantially higher than those maintained by First Bancshares.

Corporate Information

First Bancshares’ principal office is located at 310 West Wall Street, Midland, Texas 79701. FirstCapital Bank’s website is https://www.fcbtexas.com/. The information on FirstCapital Bank’s website is not part of this proxy statement/prospectus, and the reference to the FirstCapital Bank website address does not constitute incorporation by reference of any information on that website into this proxy statement/prospectus.

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BUSINESS OF LONE STAR

General

Lone Star is a Texas corporation and registered bank holding company, headquartered in Lubbock, Texas, and the sole shareholder of Lone Star Bank. Lone Star has no material business or operations at the parent company level other than owning and managing Lone Star Bank. Lone Star is subject to the supervision and regulation of the Federal Reserve and TDB.

Lone Star Bank is a Texas state bank and Federal Reserve member bank organized in 2007 and based in Lubbock, Texas. As such, the bank is subject to the supervision and regulation of the Federal Reserve and TDB. Lone Star Bank is a full-service commercial bank, providing financial services to customers primarily located in the Lubbock and Midland-Odessa market areas in Texas. As of September 30, 2022, Lone Star Bank had total assets of approximately $1.39 billion, gross loans of approximately $940.5 million, total deposits of approximately $1.25 billion, and total shareholders’ equity of approximately $134.2 million. Lone Star Bank maintains a website at www.lonestarwtx.com. The information on Lone Star Bank’s website is not part of this proxy statement/prospectus, and the reference to the Lone Star Bank website address does not constitute incorporation by reference of any information on that website into this proxy statement/prospectus.

Lone Star’s principal executive offices are located at 6220 Milwaukee Avenue, Lubbock, Texas 79424, and its telephone number at that location is (806) 771-7717.

Business

Lone Star and Lone Star Bank share a main office located at 6220 Milwaukee Avenue, Lubbock, Texas 79424. Lone Star Bank operates five banking locations, two in the Lubbock, Texas market and three in the Midland-Odessa, Texas Market. Lone Star Bank offers personal and business checking accounts, interest-bearing checking accounts, savings accounts, and various types of certificates of deposit. Lone Star Bank also offers installment loans, working capital loans, real estate loans, construction loans, residential loans, jumbo loans, commercial and home equity lines of credit, boat and auto loans, and credit cards. Lone Star Bank offers its services through a variety of channels to meet the needs of our customers including in-person through our full-service branches, automated teller machines, via telephone, online and mobile platforms.

Banking Services

Lone Star Bank is engaged in substantially all of the business operations customarily conducted by independent financial institutions in West Texas, including the acceptance of checking, savings and certificates of deposits and the making of commercial and consumer loans, real estate loans, agricultural loans and other installment and term loans. The terms of these loans vary by purpose and by type of underlying collateral, if any. The bank does a substantial amount of business with individuals, as well as with customers in small to medium-sized commercial, industrial and professional businesses. For the convenience of its customers, the bank offers drive through banking facilities, automated teller machines and online banking, as well as a suite of cash management services.

As of September 30, 2022, Lone Star Bank had approximately $940.5 million in total loans and leases. Approximately $602.1 million, or 64.0% of Lone Star Bank’s total loans were real estate loans and approximately $248.7 million, or 26.4%, of Lone Star Bank’s loans were classified as commercial and industrial loans. As of September 30, 2022, Lone Star Bank had a deposit balance of approximately $1.25 billion. Approximately $687.6 million, or 55.1%, of Lone Star Bank’s total deposits were transaction deposits, approximately $288.3 million, or 23.1%, were comprised of money market and savings accounts, and approximately $272.2 million, or 21.8%, consisted of time deposits.

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Employees

As of September 30, 2022, Lone Star Bank had 97 full-time employees, none of whom is covered by a collective bargaining agreement.

Properties

Lone Star Bank operates from its main office, located at 6220 Milwaukee Avenue, Lubbock, Texas 79424, and four full service banking offices, located in each of Big Spring, Brownfield, Midland and Odessa, Texas. Lone Star Bank owns each of its banking office locations, other than the Midland banking office, which is leased.

Legal Proceedings

There are no threatened or pending legal proceedings against Lone Star or Lone Star Bank which, if determined adversely, would, in the opinion of Lone Star management, have a material adverse effect on Lone Star’s business, financial condition, results of operations, cash flows or prospects.

Competition

Lone Star Bank operates from two full-service banking locations in the Lubbock market and three full-service banking locations in the Midland-Odessa market. The markets in which Lone Star Bank operates are highly competitive, with a number of larger and similarly sized traditional financial institutions as well as non-bank and digital bank competitors operating in each market. Many of these competitors have capital resources, geographic markets and legal lending limits substantially larger than those maintained by Lone Star Bank. In addition, many of the bank’s non-bank competitors have fewer regulatory constraints and may have lower cost structures. For purposes of this discussion, Lone Star has defined the Lubbock market as Crosby, Garza, Hale, Lubbock, Lynn and Terry Counties, Texas, and the Midland-Odessa market as Ector, Howard and Midland Counties, Texas.

As of June 30, 2022, the most recent data reported in the FDIC’s Summary of Deposits, the Lubbock banking market had 28 financial institutions operating in it, with an aggregate of 131 banking locations and approximately $13.7 billion in deposits on an unweighted basis. Lone Star Bank has two banking locations in the Lubbock banking market, comprising 3.39% of the deposit market share as of June 30, 2022.

As of June 30, 2022, the Midland-Odessa banking market had 22 financial institutions operating in it, with an aggregate of 87 banking locations and approximately $14.2 billion in deposits on an unweighted basis. Lone Star Bank has three banking locations in the Midland-Odessa banking market, comprising 5.01% of the deposit market share as of June 30, 2022.

The following table lists Lone Star Bank’s deposit market share, as reported in the FDIC’s Summary of Deposits, for each county in which Lone Star Bank has a branch, as of June 30, 2022.


County (TX)	No. of Institutions in County		Total County Deposits		Lone Star Deposits		Lone Star Deposit Market Share			Lone Star Rank
			(in thousands)		(in thousands)
Ector County		16	$	3,594,149	$	182,411		6.16	%		6
Howard County		7	$	1,391,623	$	254,882		25.54	%		2
Lubbock County		24	$	12,039,018	$	204,536		2.22	%		13
Midland County		17	$	9,201,776	$	108,946		1.45	%		11
Terry County		3	$	294,365	$	183,295		66.36	%		1

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COMPARATIVE STOCK PRICES AND DIVIDENDS

Prosperity

The following table shows (1) the market value of Prosperity common stock at the close of business on October 7, 2022, the last trading day prior to the announcement of the proposed mergers, and as of the most recent practicable date preceding the date of this proxy statement/prospectus, (2) the equivalent pro forma value of a share of First Bancshares common stock at such dates based on the value of the consideration to be received in the First Bancshares merger with respect to each share and (3) the equivalent pro forma value of a share of Lone Star common stock at such dates based on the value of the consideration to be received in the Lone Star merger with respect to each share. The equivalent prices per First Bancshares share and per Lone Star share are hypothetical implied values of the applicable merger consideration, which includes both the applicable per share stock consideration and the applicable per share cash consideration.

For illustration purposes only, if the First Bancshares merger occurs and assuming at the closing that (i) there are [ ] shares of First Bancshares common stock issued and outstanding, (ii) there are [ ] unexercised options to purchase shares of First Bancshares common stock with a weighted average exercise price of $[ ], (iii) First Bancshares’ equity capital, as calculated under the First Bancshares reorganization agreement, is equal to or greater than $204,000,000, and (iv) the price per share of Prosperity common stock received in the First Bancshares merger is equal to $[ ], which was the closing price per share of Prosperity common stock on [ ], 2023, then holders of First Bancshares common stock will receive [ ] shares of Prosperity common stock with a value of $[ ] (before adjusting for fractional shares) and $[ ] in cash for each share they own, for an aggregate implied value of $[ ] for each share of First Bancshares common stock.