Strained GaAs/InGaAs/AlGaAs quantum well structures have been grown by molecular beam epitaxy at substrate temperatures from 375 to 510 °C. The well layer thickness and In composition are analyzed by ion channeling and particle‐induced x‐ray emission as a function of growth temperature. Test structures for modulation‐doped field‐effect transistors grown at 375 and 510 °C under two different As4overpressures were also characterized by Van der Pauw measurements and low‐temperature photoluminescence. The observed differences in film quality can be explained by the influence of substrate temperature and As4flux on the cation surface mobility during growth of the InGaAs layer.