UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K/A

(Amendment No. 1)

(Mark One)

x     ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended September 30, 2021

OR

¨     TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from ______________________to ______________________

Commission File Number: 000-54986

ARCH THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code    (617) 431-2313

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

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

Common Stock, par value $0.001 per share

(Title of Class)

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ¨ No x

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes ¨ No x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes x No ¨

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes x No ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, 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 13(a) of the Securities Act. ☐

EXPLANATORY NOTE

The registrant met the “smaller reporting company”, and non-accelerated filer requirements as of the end of its 2021 fiscal year pursuant to Rule 12b-2 of the Securities Exchange Act of 1934, as amended, based upon the aggregate worldwide market value of the voting and non-voting common equity held by the registrant’s non-affiliates as of March 31, 2021.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes ¨ No x

The aggregate market value of the registrant’s voting and non-voting common equity held by non-affiliates as of the last business day of the registrant’s most recently completed second fiscal quarter, computed by reference to the average of the bid and asked price of such common equity, was approximately $32,000,000. For purposes of this calculation, it has been assumed that shares of common stock held by each director, each officer and each person who owns 10% or more of the registrant’s outstanding common stock are held by affiliates.

As of December 16, 2021, 237,169,770 shares of the registrant’s common stock were outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

None

EXPLANATORY NOTE

Arch Therapeutics, Inc. (the “Company”) is filing this Amendment No. 1 (this “Amendment”) to its Annual Report on Form 10-K for the fiscal year ended September 30, 2021, which was originally filed with the Securities and Exchange Commission on December 17, 2021 (the “Form 10-K”) to furnish Exhibits 10.50, 10.51, 10.52, 10.53 and 10.54 which were inadvertently omitted from the Form 10-K. The Company hereby amends the Form 10-K by resubmitting the corrected Exhibit Index with this Amendment.

This Amendment is an exhibit-only filing. Except for the items described above or contained in this Amendment, this Amendment continues to speak as of the date of the Form 10-K, and does not modify, amend or update any other item or disclosures in the Form 10-K, including the financial information. Accordingly, this Amendment should be read in conjunction with the Form 10-K and the Company’s other filings with the SEC.

PART IV

ITEM 15. EXHIBITS, FINANCIAL STATEMENT SCHEDULES

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.