A water‐cooled gas sampling probe capable of steady‐state operation at 15 000°K and one atmosphere has been developed. Temperature is measured by a calorimetric technique which can provide high‐accuracy calibration under arcjet conditions. The probe also measures velocity and chemical composition and, because of its small size (∼⅛ in. o.d.), is capable of accurate local measurements in the presence of severe gas‐stream property gradients. Calibrations in the partially ionized argon‐helium environment of an arcjet exhaust indicated an average agreement with mass and energy balance criteria within ½%, and a standard deviation from the mean of less than 3%.