This paper proposes a monolithic isolated gate driver design with a voltage level shifter. Incorporating voltage level converters can effectively reduce input drive voltage requirements and the overall energy needed to the power gate drivers. The on-chip transformer detailed in this study consists of a pair of on-chip inductors. Two types of the on-chip transformer structures are used: a stacked transformer (featuring higher coupling coefficient) and a tapped transformer (featuring higher voltage isolation). The on-chip transformer, full-bridge rectifier, gate driver, and voltage level converter were all produced using the TSMC 0.25-μm HV (high-voltage) CMOS process. Compared to the ündings of the previous study, simulations conducted in this study showed that the proposed monolithic isolated gate driver with a voltage level shifter required a 62% lower power input voltage and 34% less power consumption. Moreover, it could provide 12 V of output voltage and drive a load of 6000 pF with the rise and fall time less than 1 μs.