Wideband 8-12-GHz inline-type microwave power sensors that are based on measuring the microwave power coupled from the coplanar waveguide line by a microelectromechanical systems membrane are presented. In this method, the signal is available during the power detection. In order to obtain the low reflection losses and insertion losses, as well as the wideband response of the power sensor, an impedance match structure and a compensating capacitance are proposed. The fabrication of the power sensor is compatible with the GaAs monolithic microwave integrated circuit (MMIC) process. The experimental results show that the sensor has reflection losses better than 20 dB and insertion losses less than 0.45 dB up to 12 GHz. A sensitivity of more than 30 muV/mW and a resolution of 0.2 mW are obtained at the 10-GHz frequency.