Calculations were done for semiconductor heterostructures, InGaAs quantum well surrounded by GaAs waveguide layers and AlGaAs cladding layers. Finite difference method is used in solving Schrodinger equation. Temperature of the laser active region is measured. The method is based on the theory of current flow through the p-n junction. The laser mirror is investigated by thermoreflectance mapping. The method is a modulation technique, which allows for obtaining a 2-dimensional map of temperature of resolution up to single microns.