On the basis of the Seebeck effect,a terminating type MEMS microwave power sensor fully compatible with the GaAs Monolithic Microwave Integrated Circuits(MMIC) process is presented.A thermocoupler in the microwave power sensor is used to detect the temperature difference and to generate a DC voltage proportional to the microwave power.Then,a series of GaAs/Au thermocouples make up a thermopile.The sensor based on a simple principle converts the electric power into heat and the DC voltage produced by the heat is indirectly measured,so that the output microwave power can be obtained.Moreover,in order to minimize the thermal and electromagnetic losses,the bulk GaAs located beneath the device is removed through micromachining.As a result,the sensitivity of the sensor is improved.Tested results show that the HFSS simulation of S11 is less than -22 dB when the sensor measures the microwave power from -20 dBm to +20 dBm.The sensor sensitivity is higher than 0.15 mV/mW at 20 GHz,and the input return loss is less than -26 dB over the entire frequency ranges.