v3.8.0.1
Document And Entity Information - USD ($)
$ in Billions
12 Months Ended
Dec. 31, 2017
Feb. 21, 2018
Jun. 30, 2017
Document Information [Line Items]      
Entity Registrant Name MONOLITHIC POWER SYSTEMS INC    
Entity Central Index Key 0001280452    
Trading Symbol mpwr    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Well-known Seasoned Issuer Yes    
Entity Common Stock, Shares Outstanding (in shares)   42,132,242  
Entity Public Float     $ 3.1
Document Type 10-K    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Amendment Flag false