Formulas are obtained for the indirect absorption coefficient as a function of photon energy, for both degenerate and nondegenerate semiconductors, taking into account the dependence of the energy denominator on the energy of the intermediate states. The light-hole and heavy-hole contributions and the total absorption were computed for germanium. The results are displayed as a function of photon energy, in graphs, for the nondegenerate case and for several Fermi energies. The results show that, for degenerate material, absorption edges obtained by extrapolation of the experimental absorption spectrum are liable to be too low. © 1962 The American Physical Society.