Growth of AgGaSiSe4 single crystals, determination of their crystal structure, studies of electronic structure and optical properties are presented. The X-ray photoelectron core-level and valence-band spectra were measured. We recorded the X-ray emission Se K beta(2) and Ga K beta(2) bands, giving information on the energy distribution of the Se4p and Ga4p states, respectively, and compared with the X-ray photoelectron valence-band spectrum. The main contributions of the Se4p and Ga4p states have been found in the upper and central parts of the valence band, respectively, with their substantive contributions in other parts of the band. The spectral distribution of the absorption coefficient in the temperature range 100-300 K was investigated and band gap variation coefficient was evaluated (dE(g)/dT=-4.5 x 10(-4) eV/K). The activation energies of dark conductivity were calculated as follows: E-a1 = 0.03 eV, E-a2 = 0.24 eV. The IR transmission curve and the relaxation kinetics of photoinduced piezoelectric module were described. (C) 2017 Elsevier Ltd. All rights reserved.