Double heterostructures consisting of GaSb active layers with Al0.4Ga0.6Sb cladding layers were grown by molecular beam heteroepitaxy on Si substrates. The intrinsic ∼12% lattice mismatch between the GaSb and the Si at the growth temperature is largely taken up by a GaSb/AlSb superlattice. The larger thermal contraction of the GaSb layer relative to that of Si causes the GaSb layer to be under severe dilatory strain relative to the Si substrate at room temperature. Optically pumped laser emission ranging from 1.62 &mgr;m at 80 K to 1.82 &mgr;m at 350 K was observed. The threshold varied somewhat nonexponentially with temperature, with a change in slope at ∼250 K. The exponential threshold‐temperature dependences at 80 and 300 K areT0=158 and 100 K, respectively, and are higher than previously reported for GaSb lasers. At 300 K the threshold corresponds to an effective current of 12 kA/cm2.