Transphorm (TGAN) S-8 Registration of securities for employees

Exhibit 23.1

Independent Registered Public Accounting Firm’s Consent

We consent to the incorporation by reference in this Registration Statement of Transphorm, Inc. on Form S-8of our report dated March 30, 2020, which includes an explanatory paragraph as to the Company’s ability to continue as a going concern, with respect to our audits of the consolidated financial statements of Transphorm, Inc.as of and for the years ended December 31, 2019 and 2018 included in Amendment No. 2 to Form 8-K filed with the U.S. Securities and Exchange Commission on March 31, 2020.

/s/ Marcum LLP

Marcum LLP

Chicago, IL

June 1, 2020