Time‐resolved electron temperature measurements were taken behind incident normal shock waves in an arc‐driven shock tube using xenon as the test gas at an initial driven tube pressure of 0.1 Torr. At shock wave velocities from 6 to 10 km/sec, the two‐line intensity ratio technique involving the spectral lines of XeII was used to determine the electron temperature. The data indicate an electron temperature peak almost immediately behind the shock front which is well above the predicted equilibrium temperature. This peak temperature decays rapidly(∼ 1 &mgr;sec)to a plateau temperature well below the predicted equilibrium temperature. The importance of both radiative energy loss and ionizing collisions on the electron temperature decay is considered in the interpretation of the data.