Light amplifying characteristics of GaSb quantum dots embedded in Si grown on SOI were studied. Amplified spontaneous emission was observed at 6.6K under pulsed visible laser excitation. Pump power dependence of on-off gain measured in a pump-and-probe configuration showed a threshold behavior, which indicates the relevance of a three level system. At 30 K, however, gain was diminished while absorption dominated, and the photoluminescence intensity was saturated at increased pump intensities. This indicates that the interface localized electron-hole pairs providing gain have detrapped out of the interface trap due to thermal excitation and that free carrier absorption dominates at high pump. (c) 2007 Published by Elsevier B.V.