In this paper, a high accuracy, high efficiency, and wide current-sensing range current-mode PWM buck converter with on-chip current-sensing technique is presented. The proposed current-sensing circuit uses simple switch technique to achieve high accuracy, high power efficiency, and high line regulation. The test chip is fabricated using TSMC 0.18µm 1P6M 3.3V CMOS process. The measurement results show that the buck converter with on-chip current-sensing circuit can operate from 700kHz to 3MHz with a supply voltage of 1.5-5V and the output voltage of 0.5-4.5V for lithium ion battery applications. The accuracy of the proposed current-sensing circuit is exceeds 89.8% for load current from 50mA to 500mA and for temperature from 0°C to 100°C. The peak power efficiency of the buck converter is up to 95.5%.