Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 12, 2021	Jun. 30, 2020
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Registrant Name	MOSYS, INC.
Entity Central Index Key	0000890394
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
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 Drive
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
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		6,133,719
Entity Public Float			$ 6,427,310
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Undesignated Common Stock
Trading Symbol	MOSY
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Series AA Preferred Stock
Title of 12(b) Security	Series AA Preferred Stock, par value $0.01 per share
No Trading Symbol Flag	true