The strength of the hot-phonon effect generated by hot carriers in a two-dimensional heterolayer is estimated, specifically for electrons in GaAs. Both acoustic-mode phonons, at low temperature, and LO phonons are considered. For the former the phonon mean free path is taken to be large compared to the heterolayer thickness. The LO phonons are, however, assumed to decay locally. In both cases the estimates indicate that substantial hot phonon effects are to be expected in realized conditions. © 1985.