v3.19.1
Document And Entity Information - shares
3 Months Ended
Mar. 31, 2019
May 03, 2019
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 Emerging Growth Company false  
Entity Small Business false  
Entity Common Stock, Shares Outstanding (in shares)   43,057,000
Document Type 10-Q  
Document Period End Date Mar. 31, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q1  
Amendment Flag false