From measurements in the literature of the average energies, ε, required to create electron-hole pairs with ionizing radiation in several semiconductors, a value of the optical-mode deformation-potential constant, KDt, has been obtained. A recent analysis has been extended to include scattering by the polar-mode electron-phonon interaction as well as by the optical-mode deformation potential. Expressions for these scattering rates were developed in the free-particle approximation. The only unknown in the ratio of these rates is KDt. These values are KDt = 1.8 x 108 x √ρeV/cm, where ρ is the semiconductor density in gm/cm3.