A method of determining the temperature of hot gases is described that is based on the measurement of the intensity of radiation on the center of an emission line. The line is selected on the basis that it possesses blackbody intensity at the central frequency and that its width is large compared with the available spectral resolution of the optical equipment. With these conditions fulfilled, no information on the specific properties of the spectral line is required to recover temperature. The method is applied to determine the temperature behind a shock‐wave propagating into xenon gas. The temperature of the shock‐heated gas is calculated by Rankine‐Hugoniot conditions based on the measured shock velocity. A comparison between measured and theoretical temperatures is presented, and it shows improved agreement at higher temperatures and pressures. The most serious limitation on the accuracy of our implementation of this experiment is considered to be the uncertainty of the shock velocity in the presence of moderate shock attenuation.