An improved type of thin‐film heat gauge has been developed and used to measure heat‐transfer rates from a shock‐heated plasma to the end wall of a shock tube. The gauge is a resistance thermometer consisting of a triplelayered sensor coated by a moderately thick film of SiO2. It was used to measure heat transfer from nonionized argon at temperatures of up to 16 000 K. A marked increase in heat transfer at the onset of ionization near the wall indicates that the gauge can be used to obtain the contribution of free electrons to the thermal transport.