Temperature dependence of the resistivity, carrier concentration, and carrier mobility have been investigated in vacuum deposited Ag2Se thin layers. Properties of silver selenide layers developed by the reaction of poly‐ and monocrystalline parent Ag films and selenium on NaCl substrates in identical circumstances have been described and compared with one another. Experimental evidences of the hysteresis of the electrical properties due to the reversible first order transformation have been found during heating and cooling cycles. Irreversible changes of these properties in the semiconductor phase were detected. ©1995 American Institute of Physics.