A thermodynamic calculation is made of the equilibrium constant of the reactions which can occur in the H//2-GaAs-ZnSe system during heating. On the basis of this calculation, the temperature conditions of the growth of ZnSe films on GaAs substrates by the method of chemical transport reactions are determined, and a model of the transport processes in this system is proposed. Single-crystal ZnSe epitaxial films with thicknesses ranging from 450 to 75,000 A have been synthesized in process times ranging from 0. 5 to 4 hours and at H//2 flow rates equal to 200-500 cm**3/min. It is shown that these films are (GaAs)//x(ZnSe)//1// minus //x solid solutions.