AbstractInelastic scattering of electrons by optic phonons in III–V semiconducting compounds of InSb type is described, taking into account consistently nonparabolic band structure of these materials both in the ε(k) dependence and the electron wavefunctions. The calculations are based on the Kane band model, including explicitly admixture of p‐like components and spin mixing in the conduction band. A variational procedure is used to derive explicit expressions for electric conductivity in case of optic phonon scattering. It is indicated how to generalize the procedure for an arbitrary spherical energy band. Numerical values of electron mobility in n‐InSb at various temperatures and electron concentrations are presented and compared with mobilities calculated in the relaxation time approximation, thus examining the validity of the latter. It is demonstrated that even at room temperature the nonelastic character of electron–phonon collisions has a pronounced effect on the conductivity.