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In this review, the nonparabolicity of the light-hole and electron bands at the Γ-point in cubic diamond or zinc blende semiconductors is derived from Kane’s 8×8k→⋅p→ model in the large spin–orbit splitting approximation. Examples of several approximations are given with InSb as an example, and their accuracy is discussed. To determine the temperature dependence of the effective masses and the nonparabolicity parameters, the unrenormalized bandgap must be utilized. This includes only the redshift of the bandgap due to thermal expansion, not the renormalization due to deformation-potential electron-phonon coupling. As an application of this method, the chemical potential and the charge carrier concentration of intrinsic InSb are calculated from 50 to 800 K and compared with electrical and optical experiments. These results are also relevant for other semiconductors with small bandgaps as needed for mid-infrared detector applications.