A hot‐wire pyrometer for measuring gas temperatures with a high sensitivity has been developed. The method can easily be extended to measurements of surface temperature. The principal elements of a hot‐wire pyrometer are a fine wire inserted into the gas and a photomultiplier for measuring the radiation emitted from it. The output voltageVof the photomultiplier is shown both theoretically and experimentally to be the following function of wire temperatureT:V=&sgr;T7/4 exp(−&ggr;T−1/2), where &sgr; and &ggr; are the calibration constants unique to a particular system.