Spectroscopic‐ellipsometry (SE) and thermoreflectance (TR) spectra of GaAs are presented. Measurements are carried out on the same bulk sample in the 1.2–5.6 eV photon‐energy range at room temperature. These spectra are analyzed based on a simplified model of the interband transitions. Results are in satisfactory agreement with the experimental SE and TR data over the entire range of photon energies. The fact definitely links the temperature‐induced change in the dielectric function (TR) to the first derivative of the pseudodielectric function (SE). It is also concluded that the broadening terms cannot be neglected in the analysis of TR spectra. ©1995 American Institute of Physics.