Measurements of the temperature dependence of the threshold current of InGaAsP/InP lasers are presented for compositions with wavelengths λ = 1.55 and 1.65 μm. 1.55 μm lasers have been investigated with either three or four epitaxial layers to study the influence of leakage currents. The experimental results are compared with theoretical investigations which are based on the assumption that Auger recombination is responsible for the temperature behaviour. The calculation of the Auger processes is reinvestigated. Fair agreement between experiment and theory demonstrates that Auger processes are the main cause for the temperature sensitivity of InGaAsP lasers.