The high-field Hall factor of n-type germanium at 200°K has been theoretically calculated including the effect of carrier scattering into the <100> minima and that of the magnetic field dependence of the carrier temperature and population in the different valleys. The results calculated with the optical-phonon deformation-potential constant D0=0.4×109 eV cm-1 differ widely from the experimental values. Good agreement between theory and experiment is obtained for values of D0 lying within 1 × 109 and 1.5 × 109 eV cm-1. © 1971 The American Physical Society.