The temperature increase in vacuum‐evaporated films of Au and Ag was measured by allowing the evaporant to condense on the junctions of Au‐Ni thin‐film thermocouples connected in series. The (minimum) average film temperature during growth was found to depend upon the evaporation rate and the substrate temperature. The average temperature of thin films of Au and Ag during deposition can be some 400°–500°K higher than the substrate temperature; this increase is attributed to the exothermic heat of condensation and radiation heating from the evaporation source. Even at low substrate temperatures near 100°K, the average film temperature can approach 500°K. The significant temperature existing in evaporated thin films can explain grain growth phenomena and other metallurgical changes in the structure of the films.