The design of an efficient monolithic buck converter is presented in this paper. A low swing MOSFET gate drive technique is proposed that improves the efficiency characteristics of a DC-DC converter. A model of the parasitic impedances of a buck converter is developed. With this model, a design space is described which characterizes the integration of both active and passive devices of a buck converter onto the same die based on a 0.18 ?m CMOS technology. The optimum gate voltage swing of a power MOSFET that maximizes efficiency is shown to be lower than a standard full voltage swing. An efficiency of 88% at a switching frequency of 102 MHz is achieved for a voltage conversion from 1.8 volts to 0.9 volts with a low swing DC-DC converter. The power dissipation of a low swing DC-DC converter is reduced by 24.5%, improving the efficiency by 3.9% as compared to a full swing DC-DC converter.