Abstract: This paper introduces the research and progress of the MEMS microwave power sensors, whose types include the self-heating type, the indirectly-heated type, the insertion type and the capacitive type. The coplanar waveguide transmission line, the terminal resistors and the thermopile are analysed, which are basic elements of the sensor. The performances and fabrications of the microwave power sensors are described, which are based on Si and GaAs processes.