The boundary conditions of formation of Cu 2Se and Ga 2Se 3 selenides and their hydroxides have been defined by means of calculation of ionic equilibriums with use of thermodynamic constants for “gallium nitrate — copper(I) chloride — sodium selenosulphate” system, taking into account the formation of the germs of a critical radius. The possibility of hydrochemical deposition of thin Ga xCu 1-xSe yO 2-y films on two types of substrates has shown experimentally and the composition and morphology of the deposited films have studied.