Light amplifying characteristics of GaSb quantum dots embedded in Si were studied. Under visible pulsed laser excitation, a single-pass gain coefficient more than 10dBcm(-1) was obtained for planar waveguide geometry. The gain was found to decrease as the temperature increases, and eventually loss dominates beyond 25K. All electrical operations of optical amplifier were successful with a gain value of 3 dB cm(-1). © 2005 Elsevier B.V. All rights reserved.