High efficiency CMOS rectifier circuit for UHF RFID applications has been developed. The rectifier utilizes self Vth cancellation (SVC) scheme in which threshold voltage of MOSFETs is cancelled by applying gate bias voltage generated by output voltage of the rectifier itself. Very simple circuit configuration and no power dissipation feature of the scheme enable excellent power conversion efficiency (PCE) especially in small RF input power conditions. At higher RF input power conditions, PCE of the rectifier automatically decreases. This is the built-in self-power-regulation function. Proposed SVC CMOS rectifier has been fabricated with 0.35μm CMOS process and the measured performance has been compared with other types of rectifiers. The SVC CMOS rectifier achieves 29% PCE at -9.9dBm RF input power condition. This PCE is larger than ever reported rectifiers under the condition.