UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-A

FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES

PURSUANT TO SECTION 12(b) OR 12(g) OF

THE SECURITIES EXCHANGE ACT OF 1934

FG MERGER III CORP.

(Exact name of registrant as specified in its charter)

Securities to be registered pursuant to Section 12(b) of the Act:

If this form relates to the registration of a class of securities pursuant to Section 12(b) of the Exchange Act and is effective pursuant to General Instruction A.(c) or (e), check the following box. x

If this form relates to the registration of a class of securities pursuant to Section 12(g) of the Exchange Act and is effective pursuant to General Instruction A.(d) or (e), check the following box. ¨

If this form relates to the registration of a class of securities concurrently with a Regulation A offering, check the following box. ¨

Securities Act registration statement file number to which this form relates:

333-287670

Securities to be registered pursuant to Section 12(g) of the Act:

None

Item 1. Description of Registrant’s Securities to be Registered

The securities to be registered hereby are units, common stock, par value $0.0001 per share, and redeemable warrants to purchase common stock of FG Merger III Corp., a Nevada corporation (the “Registrant”). The description of the units (each consisting of one share of common stock, $0.0001 par value per share, and one-half of one redeemable warrant), the common stock and the warrants (each whole warrant exercisable for one share of common stock at an exercise price of $11.50) of Registrant, as set forth under the caption “Description of Securities” in the prospectus forming a part of the Registration Statement on Form S-1, as originally filed with the Securities and Exchange Commission (the “Commission”) on May 30, 2025 (Registration No. 333-287670), including exhibits, and as subsequently amended from time to time (the “Registration Statement”), is hereby incorporated by reference. In addition, the above-referenced description included in any prospectus relating to the Registration Statement filed with the Commission pursuant to Rule 424(b) under the Securities Act of 1933, as amended, shall be deemed to be incorporated by reference herein.

Item 2. Exhibits

Pursuant to the Instructions as to Exhibits for Form 8-A, no exhibits are required to be filed, because no other securities of the Registrant are registered on the NASDAQ Stock Market LLC, and the securities registered hereby are not being registered pursuant to Section 12(g) of the Securities Exchange Act of 1934, as amended.

SIGNATURE

Pursuant to the requirements of Section 12 of the Securities Exchange Act of 1934, the registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereto duly authorized.