A coaxial power sensor assembly configured to provide a broadband matched termination utilizing coplanar waveguide topology while simultaneously providing a source of heat energy for a surface mount chip thermistor element to measure applied input power. The coaxial thermal power sensor is comprised of a thin film resistive device on a dielectric substrate and a surface mount chip thermistor element placed in close planar proximity to the resistive device in order to maximize the heat flux via a closely coupled thermal path to the thermistor and alter the bias current through the resistance to be measured. The power sensor is intended to function from DC to 70 GHz, but the same should not be construed as a limitation.