A complete design strategy (mechanical and electrical) for a 25 W 28 V/5 V dc-dc converter utilizing SiC and SOI electronics is presented. The converter includes a high-temperature SOI-based PWM controller featuring 150 kHz operation, a PID feedback loop, maximum duty cycle limit, complementary or symmetrical outputs, and a bootstrapped high-side gate driver. Several passive technologies were investigated for both control and power sections. Capacitor technologies were characterized over temperature and over time at 300 C ∘ , power inductors designed and tested up to 350 C ∘ , and power transformers designed and tested up to 500 C ∘ . Northrop Grumman normally-off SiC JFETs were used as power switches and were characterized up to 250 C ∘ . Efficiency and mass optimization routines were developed with the data gained from the first prototype. The effects of radiation on SiC and SOI electronics are then discussed. The results of the first prototype module are presented, with operation from 25 C ∘ up to an ambient temperature of 240 C ∘ .