Temperature dependence of threshold in 1.3 &mgr;m semiconductor lasers is analyzed in terms of contributions due to gain, internal efficiency, internal loss, and nonradiative recombination. Rapid decrease of differential gain and roughly proportional increase in transparency carrier density are determined to dominate temperature dependence of threshold current. Auger recombination is found to play a secondary role in reducingT0by compounding the effects of rapidly increasing threshold carrier density. ©1995 American Institute of Physics.