We present 4.5 , 8 , and 16µm photometry from the Spitzer Space Telescope for 204 stars in the Upper Scorpius OB Association .
The data are used to investigate the frequency and properties of circumstellar disks around stars with masses between \sim 0.1 and 20 M _ { \odot } at an age of \sim 5 Myr .
We identify 35 stars that have emission at 8µm or 16µm in excess of the stellar photosphere .
The lower mass stars ( \sim 0.1-1.2 M _ { \odot } ) appear surrounded by primordial optically thick disks based on the excess emission characteristics .
Stars more massive than \sim 1.8 M _ { \odot } have lower fractional excess luminosities suggesting that the inner \sim 10 AU of the disk has been largely depleted of primordial material .
None of the G and F stars ( \sim 1.2-1.8 M _ { \odot } ) in our sample have an infrared excess at wavelengths \leq 16µm .
These results indicate that the mechanisms for dispersing primordial optically thick disks operate less efficiently on average for low mass stars , and that longer time scales are available for the buildup of planetary systems in the terrestrial zone for stars with masses \mathbin { \lower 3.0 pt \hbox { $ \hbox to 0.0 pt { \raise 5.0 pt \hbox { $ \char 60 $ } } % \mathchar 29208 $ } } 1 M _ { \odot } .