The catalytic reforming of hydrocarbons in a microreformer is an attractive approach to supply hydrogen to fuel cells while avoiding storage and safety issues. High-surface-area catalyst supports must be stable above 800 degrees C to avoid catalyst coking; however, many porous materials lose their high surface areas below 800 degrees C. This paper describes an approach to fabricate macroporous silicon carbonitride (SiCN) and silicon carbide (SiC) monoliths with geometric surface areas of 10(5) to 10(8) m(2) per m(3) that are stable up to 1200 degrees C. These structures are fabricated by capillary filling of packed beds of polystyrene or silica spheres with low-viscosity preceramic polymers. Subsequent curing, pyrolysis, and removal of the spheres yielded SiCN and SiC inverted beaded monoliths with a chemical composition and pore morphology that are stable in air at 1200 degrees C. Thus, these structures are promising as catalyst supports for high-temperature fuel reforming.