Abstract The electronic structure and chemical bonding in HgGa 2S 4 crystals grown by vapor transport method are investigated with X-ray photoemission spectroscopy. The valence band of HgGa 2S 4 is found to be formed by splitted S 3p and Hg 6s states at binding energies BE=3–7 eV and the components at BE=7–11 eV generated by the hybridization of S 3s and Ga 4s states with a strong contribution from the Hg 5d states. At higher binding energies the emission lines related to the Hg 4f, Ga 3p, S 2p, S 2s, Hg 4d, Ga LMM, Ga 3p and S LMM states are analyzed in the photoemission spectrum. The measured core level binding energies are compared with those of HgS, GaS, AgGaS 2 and SrGa 2S 4 compounds. The valence band spectrum proves to be independent on the technological conditions of crystal growth. In contrast to the valence band spectrum, the distribution of electron states in the bandgap of HgGa 2S 4 crystals is found to be strongly dependent upon the technological conditions of crystal growth as demonstrated by the photoluminescence analysis.