As filed with the Securities and Exchange Commission on August 20, 2025 Registration No. 333-289549 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 AMENDMENT NO. 1 TO FORM S-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 CLEARSIGN TECHNOLOGIES CORPORATION (Exact name of registrant as specified in its charter) (State or other jurisdiction of incorporation or organization) (Primary Standard Industrial Delaware 3823 26-2056298 (I.R.S. Employer Identification No.) 8023 East 63 ...

As filed with the Securities and Exchange Commission on August 12, 2025 Registration No. 333- UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 CLEARSIGN TECHNOLOGIES CORPORATION (Exact name of registrant as specified in its charter) (State or other jurisdiction of incorporation or organization) Delaware 3823 26-2056298 (Primary Standard Industrial Classification Code Number) (I.R.S. Employer Identification No.) 8023 East ...