Exhibit 5.1

DLA Piper LLP (US) 555 Mission St. #2400 San Francisco, California 94105 www.dlapiper.com

November 24, 2023

GigCapital5, Inc.

1731 Embarcadero Rd., Suite 200

Palo Alto, CA 94303

Ladies and Gentlemen:

We have acted as counsel to GigCapital5, Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing by the Company with the U.S. Securities and Exchange Commission (the “Commission”) of a registration statement on Form S-4, Registration No. 333-269760 (as amended, the “Registration Statement”) and the related proxy statement/prospectus relating to the registration under the Securities Act of 1933, as amended (the “Securities Act”), of the shares of the Company’s Common Stock, par value $0.0001 per share (the “Common Stock”), to be issued by the Company pursuant to the terms of the Business Combination Agreement, dated as of December 8, 2022 (as it may be amended and/or restated from time to time, the “Business Combination Agreement”), by and among the Company, QTI Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of the Company, and QT Imaging, Inc., a Delaware corporation (“QT Imaging”). Unless otherwise indicated, each capitalized term used herein has the meaning ascribed to it in the Registration Statement.

This opinion letter is furnished in accordance with the requirements of Item 601(b)(5) of Regulation S–K under the Securities Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement, the related proxy statement/prospectus, or any proxy statement/prospectus filed pursuant to Rule 424(b) with respect thereto, other than as expressly stated herein with respect to the issuance of the Common Stock.

In connection with our opinion expressed below, we have examined originals or copies, certified or otherwise identified to our satisfaction, of the following documents and such other documents, corporate records, certificates and other statements of government officials and corporate officers of the Company as we deemed necessary for the purposes of the opinion set forth in this opinion letter:

(a) the Registration Statement;

(b) the Business Combination Agreement (filed as Exhibit 2.1 to the Registration Statement);

(c) the form of Second Amended and Restated Certificate of Incorporation of the Company, to become effective upon consummation of the Business Combination (included as Annex B to the proxy statement/prospectus included in the Registration Statement);

(d) the form of amended and restated bylaws of the Company, to become effective upon consummation of the Business Combination (included as Annex H to the proxy statement/prospectus included in the Registration Statement);

(e) a copy of the Minutes of the special meeting of the Board of Directors of the Company, dated as of December 4, 2022; and

(f) the specimen common stock certificate of the Company.

We have relied, to the extent we deem such reliance proper, upon such certificates or comparable documents of officers and representatives of the Company and of public officials, and upon statements and information furnished by officers and representatives of the Company, with respect to the accuracy of material factual matters contained therein. In rendering the opinion expressed below, we have assumed, without independent investigation or verification of any kind, the genuineness of all signatures on documents we have reviewed, the legal capacity and competency of all natural persons signing all such documents, the authenticity and completeness of all documents submitted to us as originals, the conformity to authentic, complete original documents of all documents submitted to us as copies, the truthfulness, completeness and correctness of all factual representations and statements contained in all documents we have reviewed, the accuracy and completeness of all public records examined by us, and the accuracy of all statements in certificates of officers of the Company that we reviewed.

Based upon the foregoing assumptions, and subject to the qualifications and limitations stated herein, we are of the opinion that: the shares of Common Stock to be issued by the Company pursuant to and in the manner contemplated by the terms of the Business Combination Agreement will, upon issuance, be duly authorized and, when issued upon the terms and conditions set forth in the Registration Statement and the Business Combination Agreement, such shares of Common Stock will be validly issued, fully paid and nonassessable.

We express no opinion concerning any law other than the Delaware General Corporation Law (including the statutory provisions, all applicable provisions of the Delaware Constitution and the reported judicial decisions interpreting the foregoing) and the federal law of the United States of America.

This opinion letter is for your benefit in connection with the Registration Statement, and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Securities Act.

The opinion expressed above is as of the date hereof only, and we express no opinion as to, and assume no responsibility for, the effect of any fact or circumstance occurring, or of which we learn, subsequent to the date of this opinion letter, including, without limitation, legislative and other changes in the law or changes in circumstances affecting any party. We assume no responsibility to update this opinion letter for, or to advise you of, any such facts or circumstances of which we become aware, regardless of whether or not they affect the opinion expressed in this opinion letter.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement, and to the reference to our firm as counsel for the Company that has passed on the validity of the Common Stock appearing under the caption “Legal Matters” in the proxy statement/prospectus forming part of the Registration Statement, and in any proxy statement/prospectus filed pursuant to Rule 424(b) with respect thereto. In giving this consent, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or under the rules and regulations of the Commission thereunder (including Item 509 of Regulation S-K).

Very truly yours,

/s/ DLA Piper LLP (US)