v3.19.2
Document And Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 29, 2019
Document Information [Line Items]    
Entity Central Index Key 0001280452  
Entity Shell Company false  
Entity Registrant Name MONOLITHIC POWER SYSTEMS INC  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q2  
Document Fiscal Year Focus 2019  
Entity Small Business false  
Entity Emerging Growth Company false  
Document Quarterly Report true  
Document Transition Report false  
Document Type 10-Q  
Document Period End Date Jun. 30, 2019  
Entity File Number 000-51026  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 77-0466789  
Entity Address, Address Line One 4040 Lake Washington Blvd. NE, Suite 201  
Entity Address, City or Town Kirkland  
Entity Address, State or Province WA  
Entity Address, Postal Zip Code 98033  
City Area Code 425  
Local Phone Number 296-9956  
Title of 12(b) Security Common Stock  
Trading Symbol MPWR  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   43,244,000