Abstract: Thermistor-type power meters use DC substitution to measure microwave and millimeter wave power. To compensate for environmental temperature changes, these power meters typically employ both measurement and compensation bridges, operating in a dual-bridge mode. When calibrating a coaxial thermistor-type power sensor using a microcalorimeter power standard, the measurement bridge alone cannot be used, even with stable environmental temperatures. To ensure valid calibration results, both environmental temperature compensation and ceramic core temperature variation compensation (due to dual-element errors) are necessary. Experiments show that at 18 GHz and 10 mW power level, the substituted power deviation for an N-type coaxial thermistor power sensor is 0.38% when measured with single versus dual-bridge power meters. For waveguide thermistor-type power sensors with single-element structures, calibrating effective efficiency does not require consideration of single versus dual-bridge measurement issues.