A Aigh efficiency differential CMOS rectifier circuit for UHF RFIDs was developed. The rectifier has a cross-coupled bridge configuration and is driven by a differential RF input. Differential-drive topology enables simultaneous low ON-resistance and small reverse leakage of diode-connected MOS transistors, resulting in large power conversion efficiency (PCE), especially under small RF input power conditions. The differential-drive rectifier was fabricated with 0.18-μm CMOS technology, and the measured performance was compared with those of other types of rectifiers. Dependence of the PCE on an input RF signal frequency and output loading conditions was also evaluated. 66% of PCE was achieved under conditions of 953 MHz, -12 dBm RF input and 10 Kω DC output load. This is twice as large as that of the state-of-the-art rectifier circuit. The peak PCE increases with a decrease in operation frequency and with an increase in output load resistance.