| Cover | Nov. 11, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | MOSYS, INC. |
| Entity Central Index Key | 0000890394 |
| Document Type | 8-K |
| Amendment Flag | false |
| Entity Emerging Growth Company | false |
| Document Period End Date | Nov. 11, 2021 |
| Entity File Number | 000-32929 |
| Entity Incorporation State Country Code | DE |
| Entity Tax Identification Number | 77-0291941 |
| Entity Address Address Line 1 | 2309 Bering Dr. |
| Entity Address City Or Town | San Jose |
| Entity Address State Or Province | CA |
| Entity Address Postal Zip Code | 95131 |
| City Area Code | 408 |
| Local Phone Number | 418-7500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.001 per share |
| Trading Symbol | MOSY |
| Security Exchange Name | NASDAQ |
