DC-DC converters are critical building blocks in energy harvesting systems which are applied to provide the energy for the implantable biomedical devices. They are required to meet very strict specifications and consume as less power as possible. Therefore, their power conversion efficiency and stability of the functionality in the varying environment become the major considerations in this thesis project, the target of which is to design a DC-DC converter for energy harvesting applications. The conventional PWM control is not usually suitable for the DC-DC converters applied in energy harvesting applications because of its bad stability and low power conversion efficiency over wide input voltage and load current ranges. It is demonstrated that the adaptive on-time/off-time (AOOT) control proposed in this thesis is an excellent alternative to deal with the issue and the zero current switching (ZCS) adjustment technique can be applied to improve further the performance of the DC-DC converter by the fine tuning of the off-time. In this thesis, a systematic design flow of a boost DC-DC converter has been presented from the design of the power plant, to the selection of the most suitable control technique, then to the transistor-level implementation and finally to the layout design. Moreover, the circuitry of a boost DC-DC converter and the layout of its most parts have been implemented in TSMC 40nm CMOS process. The post-layout simulation results prove that the proposed boost DC-DC converter can generate a stable 1V output voltage with very small ripples (