Thin films of binary semiconductor compound HgSe are of interest as materials for basic research due to its unusual band structure, as well as for practical use as IR detectors, IR emitters, tunable lasers, ultrasonic and gas sensors, catalysts, reflective materials, transducers of solar energy. Existing methods of producing semiconductor HgSe layers include physical and chemical principles. Itis noted that chemical precipitation of mercury selenide with sodium selenosulfate, which excludes the formation of metal cyanamide, is promising method. Based on the idea of the reversible nature of the hydrolytic decomposition of sodium selenosulfate in aqueous solutions, a thermodynamic analysis of the conditions for the deposition of the mainZnSe and impurity Zn(OH)2 solid phases was carried out in the alkaline systems “Hg(NO3)2 - NH4SCN - Na2SeSO3” and “Hg(NO3)2 - NH4SCN - NH4I - Na2SeSO3” (pH = 8.9), and their boundary conditions of formation were established.The possibility of controlling the process of hydrochemical deposition of a film of mercury selenide, in particular, the preparation of nano-crystalline selenide of mercury by introducing an additional ligand, ammonium iodide, was experimentally shown...