A DC-DC regulator is proposed to attach to the battery-less solar tag applied in the Internet of Things (IoTs) market. Two main purposes in this design is to maximize the power transfer efficiency and to provide a high voltage supply to the back-end circuit. The overall circuit consists of the cross-coupled charge pump, optimal power point tracking and timing control circuit. It is expected to boost the input voltage from 0.55-0.65V to the output of 1-1.1V at 80-100μW condition. Gated PFM circuit is adopted in the optimal power point tracking system to modulate the input frequency of the charge pump to match the inner resistance of the solar cell. This system has been taped-out by TSMC 0.18UM 1P6M process twice and N-fab 0.35UM process once. The experimental results of this chip show that the voltage conversion efficiency (VCE) is 97% and the power conversion efficiency (PCE) is 11.7% at 30μW input power condition. The reason of the low efficiency has been found and improved by enhancing the pumping capacitance. The efficiency of the 3rd tape-out in N-fab has been improved to 81.2% according to the simulation results.