UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 9)*

DIODES INCORPORATED

(Name of Issuer)

Common Stock, $0.66 ²⁄₃ Par Value

(Title of Class of Securities)

254543 10 1

(CUSIP Number)

Richard D. White

Chief Financial Officer

4949 Hedgcoxe Road, Suite 200, Plano, Texas 75024

(972) 987-3900

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

August 12, 2014

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D/A

This Schedule 13D, Amendment No. 9, dated August 12, 2014, (“Amendment No. 9”), amends and supplements the Schedule 13D dated February 1, 1990, the Schedule 13D, Amendment No. 1, dated March 5, 1990 (“Amendment No. 1”), the Schedule 13D, Amendment No. 2, dated December 6, 1991 (“Amendment No. 2”), the Schedule 13D, Amendment No. 3, dated May 4, 1993 (“Amendment No. 3”), the Schedule 13D, Amendment No. 4, dated April 10, 1994 (“Amendment No. 4”), the Schedule 13D, Amendment No. 5, dated August 10, 1995 (“Amendment No. 5”) and the Schedule 13D, Amendment No. 6, dated July 8, 1997 (“Amendment No. 6”), filed by Silitek Corporation, a Taiwan, Republic of China corporation (“Silitek”), the Schedule 13D, Amendment No.7, dated November 22, 2005 (“Amendment No. 7”), and the Schedule 13D, Amendment No. 8, dated February 26, 2009, filed by Lite-On Semiconductor Corporation, a Taiwan, Republic of China corporation (“Lite-On Semiconductor”).

Except as otherwise set forth in this Amendment No. 9, all of the information reported in the Schedule 13D and Amendment Nos. 1, 2, 3, 4, 5, 6, 7 and 8 is hereby incorporated in this Amendment No. 9. Capitalized terms not otherwise defined herein shall have the same meanings given them in Schedule 13D and Amendment Nos. 1, 2, 3, 4, 5, 6, 7 and 8.

(a) The name of the issuer is Diodes Incorporated (the “Issuer” or “Diodes”).

(b) The address of the Issuer’s principal executive office is 4949 Hedgcoxe Road, Suite 200, Plano, Texas 75024.

(c) The title of the class of securities to which this statement relates is the Common Stock, par value $0.66 ²⁄₃ of the Issuer (the “Common Stock”).

(a) The Common Stock to which this Amendment No. 9 relates is held in the name of Lite-On Semiconductor.

(b) The principal office of Lite-On Semiconductor is located at 9F. No. 233-2, Pao-Chiao Road, Hsin-Tien, New Taipei City 23145, Taiwan, Republic of China.

(c) Lite-On Semiconductor is engaged in the manufacture and sale of electronic components and equipment, including semiconductor rectifiers. Diodes is a leading global manufacturer and supplier of high-quality application specific standard products within the broad discrete, logic and analog semiconductor markets.

(d) – (f) Not applicable.

Not applicable.

The information in Item 4 of the Schedule 13D is hereby amended by adding the following:

During the period from August 12 to August 26, 2014, Lite-On Semiconductor sold an aggregate amount of 300,000 shares of the Common Stock in the open market.

(a) Following the event to which this Amendment No. 9 relates, Lite-On Semiconductor owned beneficially, 8,065,778 shares of Common Stock. This total number of shares of Common Stock owned by Lite-On Semiconductor represents 17.1 percent of the Common Stock of Diodes outstanding based upon the number of shares of Common Stock outstanding as contained in the Issuer’s Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2014.

(b) Lite-On Semiconductor has the sole power to vote and dispose of 8,065,778 shares of Common Stock.

(c) There have been no other transactions that were effected during the past 60 days by Lite-On Semiconductor.

(d) – (e) Not applicable.

There are no contracts, arrangements, understandings or relationships (legal or otherwise) among the persons named in Item 2 and between such persons and any person with respect to any securities of the Issuer except as otherwise set forth herein.

Not applicable.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: September 5, 2014