A microwave power detector based on a single metal-oxide-semiconductor field effect transistor (MOSFET) fully compatible with standard CMOS process is presented. The detector uses the nonlinearity of the channel resistance of a MOSFET operating in ohmic regime to rectify the microwave signal. A first prototype shows a sensitivity below mW and a good linearity over at least two decades of microwave power. The absence of additional technological steps required for the detector fabrication with respect to a standard CMOS process opens the realm of RF power monitoring in products at virtually no cost.