The valence band of ZnS, SrS, and Sr0.45Ca0.55Ga2S4 thin film phosphors were measured by x-ray photoelectron spectroscopy. The valence band spectrum from polycrystalline ZnS film compared favorably with that previously reported for ZnS single crystals, and with calculated theoretical densities of states (after convolution with a Gaussian curve). The SrS valence band spectrum exhibited three peaks, which generally agree with the expected densities of states. The St(0.45)Ca(0.55)Ga(2)S(4) spectrum features were much less intense, consistent with the film being amorphous.