Probe and recombination‐radiation spectrum measurements were used to measure the electron number density and temperature profiles in front of a flat disc in a supersonic seeded‐gas plasma. The region of interest extended several body diameters upstream of the disc and through the shock wave. The experiment covered a free stream electron density range of 4 × 1011to 1.6 × 1012cm−3and an electron temperature range of 0.06 to 0.1 eV. The region of reduced luminosity upstream of the shock wave is shown to be associated with electron heating at constant electron density. The electron thermal conductivity is derived from measurements in the upstream region and gives reasonable agreement with the Spitzer formula. Measurements are made of the electron temperature change across the heavy‐particle shock wave and of the over‐all electron temperature ratio across the entire process. It is shown that the over‐all electron‐temperature ratio could not be predicted on the basis of an adiabatic one‐demensional flow process in this experiment.