Hot-carrier solar cells may yield very high efficiency if the heat transfer from electrons to phonons is low enough. In this paper we calculate this heat transfer for the two inelastic mechanisms known to limit the electric conductivity: the multi-valley scattering in non-polar semiconductors and the coupling of electrons to longitudinal optical phonons in polar semiconductors. Heat transfer is ruled by matrix elements deduced from electric conductivity measurements. The cell power extracted from hot-carrier solar cells affected by this mechanism, but otherwise ideal, is deduced. It is found that Si and Ge solar cells, mainly under concentrated Sun light, might lead to better efficiencies than conventional cells. (C) 2009 Elsevier B.V. All rights reserved.