Abstract: One of the ways of power semiconductor devices PSD efficiency increase is the evaporative cooling of PSD using thermal syphons. In this study, we consider the developed technique of thermal resistance calculation on the heat flow path from the evaporator surface to the external environment of a thermal syphon cooling air with a two-component internal heat carrier. The analysis of the obtained formulas makes it possible to reveal the most significant factors affecting the thermal resistance of a thermal syphon.