| Document and Entity Information | Sep. 14, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Sep. 14, 2021 |
| Entity Registrant Name | MOSYS, INC. |
| Entity Central Index Key | 0000890394 |
| Trading Symbol | MOSY |
| Entity Emerging Growth Company | false |
| Entity Address, State or Province | CA |
| Title of 12(b) Security | Common Stock, par value $0.001 per share |
| Security Exchange Name | NASDAQ |
| Entity File Number | 000-32929 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 77-0291941 |
| Entity Address, Address Line One | 2309 Bering Dr. |
| Entity Address, City or Town | San Jose |
| Entity Address, Postal Zip Code | 95131 |
| City Area Code | 408 |
| Local Phone Number | 418-7500 |
| Written Communications | false |
| Soliciting Material | true |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
