This work focuses on the implementation of a thermistor-based power sensor for an operating frequency around 77 GHz in a 0.35 m bipolar technology. As the sensor concept is based on DC substitution, absolute rms power levels can be derived which makes the sensor suitable for built-in self-test and calibration purposes. The error between the sensor results and a radio frequency reference measurement is as small as 0.5 dB for power levels larger than -5 dBm.