| Document and Entity Information | Mar. 01, 2024 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001715768 |
| Document Type | 8-K |
| Document Period End Date | Mar. 01, 2024 |
| Entity Registrant Name | Transphorm, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-41295 |
| Entity Tax Identification Number | 82-1858829 |
| Entity Address, Address Line One | 75 Castilian Drive |
| Entity Address, City or Town | Goleta |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 93117 |
| City Area Code | (805) |
| Local Phone Number | 456-1300 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | TGAN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
