The temperature dependence of threshold current of strained quantum well lasers is analyzed both experimentally and theoretically. The measurements are performed on ridge waveguide In0.2Ga0.8As/GaAs multiquantum well lasers emitting near 1 &mgr;m. The carrier densities at threshold of these lasers are measured using very short current pulse injection. A simplified calculation of the radiative, nonradiative recombination rates and the relationship between gain and carrier density in strained quantum well lasers is described. The results of the calculation are compared with experimental results.