This paper presents a high-efficiency monolithic dc-dc PFM boost converter designed with a standard TSMC 3.3/5V 0.35 μm CMOS technology. The proposed boost converter combines the parallel power MOS technique with pulse-frequency modulation (PFM) technique to achieve high efficiency over a wide load current range, extending battery life and reducing the cost for the portable systems. The proposed parallel power MOS controller and load current detector exactly determine the size of power MOS to increase power conversion efficiency in different loads. Postlayout simulation results of the designed circuit show that the power conversion is 74.9–90.7% efficiency over a load range from 1 mA to 420 mA with 1.5 V supply. Moreover, the proposed boost converter has a smaller area and lower cost than those of the existing boost converter circuits.