Fully microscopic many-body models are used to investigate the temperature dependence of radiative and Auger losses in semiconductor lasers. Classical estimates based on simplified models predict carrier density independent temperature dependencies, 1/T for the radiative losses and a temperature activated exponential dependence for the Auger losses. Instead, the microscopic models reveal for the example of a typical InGaAsP-based structure a 1/T 3-dependence for the radiative losses at low carrier densities. For high densities this dependence becomes much weaker and deviates from a simple power law. Auger losses can be described by an exponential dependence for limited temperature ranges if a density dependent activation energy is used. For the threshold carrier density a temperature dependence close to T2 is found instead of the linear temperature dependence assumed by the simplified models.