Future aircraft and more-electric propulsion architectures impose rapidly growing heat loads on engines, power electronics, and fuel systems. There is a critical need for compact, lightweight heat-transport elements that can operate at high pressure and temperature while integrating cleanly into advanced power and thermal management systems. We are investigating microchannel diffusion-bonded heat exchangers (MCDHX) that couple hot engine air with cold fuel—such as Jet-A, sustainable aviation fuel (SAF) blends, or even cryogenic hydrogen—to provide aggressive heat rejection and fuel conditioning in aircraft-relevant environments. By combining high-effectiveness microchannel geometries with robust diffusion-bonded construction, MCDHXs offer a promising path toward meeting the thermal management and fuel system performance targets for next-generation aircraft.