Abstract: In this paper, A kind of low-voltage high-efficient on-chip current sensing circuit for monolithic current- mode switch DC/DC converter is proposed. The circuit makes use of power transistor equivalent resistor current sensing technique and source-input differential voltage amplification technique. As a result, the power supply range can be as low as 2. 3V, -- 3dB bandwidth is up to 12 MHz and the quiescent current peak is only 19~A under maximum load current, which is about I. 5 orders lower than the quiescent current peak using traditional power transistor mirror-current sensing. The converter is designed and fabricated in 0.5~tm 2P3M Mixed Signal CMOS process. The test results show that the maximum sensing current of 1.1A, minimum power supply voltage of the converter is 2.3V, the conversion efficiency is higher than 93% under heavy load.