The measured temperature coefficients of the energy separations between the Ga 3d core levels and the top (Γ8V) and bottom (X6C) of the sp3 valence and conduction bands in GaP between 110 K and 295 K are (+1.0±0.5)×10−4 eV K−1and (-2.4±0.5)×10−4 eV K−1, respectively. They are described within experimental accuracy by the Debye-Waller, hydrostatic, self-energy, and spatially averaged screened-ion core potential interactions of the sp3 bands alone. No significant core-level contribution is observed.