Abstract This work is for the first time an experimental study of thermal characteristics of an copper gravity heat pipe (thermosyrhon) with an outer diameter of 12 mm and a length of 230 mm with a threaded evaporator and freon R141b as working fluid under natural convection. The study demonstrates how a change in power input in the range from 5 W to 70 W (with a 5 W step) at natural convection affects such thermal characteristics of the gravity heat pipe (GPH) as temperature in evaporator section, temperature distribution along the length of the GPH, total thermal resistance, thermal resistance in evaporation and condensation sections, and heat transfer coefficients in evaporation and condensation sections. Also studied is the influence of tilt angle of the GPH changing from 0 to 90° (with a 15° step) on its thermal characteristics. The coefficient of convective heat exchange between the heat sink and air at different values of heat flux and tilt angle is determined experimentally. The obtained research results indicate that the GPH with a threaded evaporator can be effectively used in natural air cooling systems for electronic equipment with high heat flux values, for example, LED devices, power amplifiers of T/R modules, etc.