We have developed a novel metal-semiconductor field-effect-transistor (MESFET) technology suitable for extreme environment electronics. The MESFET technology is fully CMOS-compatible and can be integrated alongside conventional MOSFETs with no changes to the process flow. Unlike the MOSFETs however, the MESFETs do not require a fragile metal-oxide-semiconductor (MOS) interface and are extremely robust. With breakdown voltages in the range 10-50V the MESFET operating voltage greatly exceeds that of the accompanying CMOS. The combination of CMOS compatibility with high breakdown voltage allows for integrated DC-to-DC power conversion solutions that would otherwise require discrete components based on laterally diffused metal-oxide-semiconductor (LDMOS) devices. The MESFETs are intrinsically radiation tolerant up to 1 Mrad(Si) and have been demonstrated to work over the temperature range -196C to +150C. The Phase 1 R&D we are proposing will characterize the large signal switching performance of the SOI MESFETs for buck converter applications in extreme environments.