Highly sensitive rectifier based on a new operation principle is presented. The rectifier modified from a standard single-shunt diode rectifier employs a series inductor. The inductor is optimized so as to resonate with the diode parasitic capacitance, thereby enhancing the induced electromotive force of the inductor to effectively reduce the threshold voltage of the diode. The resonance also leads to self-compensation of the reflection, enabling to make full use of the weak input RF signal. Despite the simple circuit configuration, the minimum RF input power required for rectification is reduced by more than two orders of magnitude. A prototype 2.45-GHz rectifier was fabricated using commercial packaged diode, demonstrating 28% RF-DC conversion efficiency and 5% reflectance for RF input power of -20 dBm.