The aim of this paper is to review some of the models and solution techniques used in the simulation of high-power semiconductor lasers and to address open questions. We discuss some of the peculiarities in the description of the optical field of wide-aperture lasers. As an example, the role of the substrate as a competing waveguide in GaAs-based lasers is studied. The governing equations for the investigation of modal instabilities and filamentation effects are presented and the impact of the thermal-lensing effect on the spatiotemporal behavior of the optical field is demonstrated. We reveal the factors that limit the output power at very high injection currents based on a numerical solution of the thermodynamic based drift-diffusion equations and elucidate the role of longitudinal spatial hole burning.