A PCB embedded transformer for harsh environment (i.e., ambient temperature above 200 • C) applications is presented and used in the design of a 2 MHz integrated power-supply prototype for gate driver. The main benefits of using this developed PCB embedding process are the capability to customize the air-gap for the flyback transformer and volume reduction for the converter. The easy modulation of the air-gap distance can be achieved using PCB material in specfic thickness. Moreover, the design of a coplanar-winding transformer structure with very low inter-winding capacitance needs a large winding area and raises the interest for the PCB integration approach. Two-machined ferrite pieces in UI shape were sandwiched into a multi-layer PCB laminate with multiple pressing processes. A converter prototype built with the PCB embedded transformer and other components (GaN transistors, gate driver and passives) mounted above it shows 72% of power efficiency. One thousand thermal cycles between −55 • C and 200 • C were performed on the PCB embedded transformer without observation of any major defects, such as delamination and cracking. The thermal reliability test validates the compatibility between the selected ferrite core and PCB materials as well as the feasibility of this developed transformer embedding method. A three-time volume reduction is achieved when comparing with a benchmark converter prototype using discrete transformer.