The temperature sensitivity of both strained and lattice-matched 1.5 mum quantum well lasers has been studied. From a complete experimental investigation of the temperature behavior of carrier lifetime, gain, and internal loss, it is found that Auger recombination is not the dominant factor in affecting the temperature sensitivity of threshold currents in 1.5 mum lasers. Instead, the dominant contribution to the temperature dependence of threshold currents in 1.5 mum lasers is the change in differential gain with temperature-a characteristic not improved by strain.