The active oxidation of SiC has been studied at 1390 and 1490 degrees C, paying particular attention to the active-to-passive and passive-to-active transition points. First the active-to-passive transition for pure silicon was studied at 1290 degrees C. The beginning of passivity is characterized by micron-sized SiO2 rod formation on the surface due to the oxidation of SiO(g), consistent with other investigators. These rods were not observed in the active-to-passive transition for SiC; but they were observed in the passive-to-active transition for SiC. This type of microstructure yields information about the breakdown of the passive film. Unlike pure silicon, at a fixed temperature a substantial difference in the transition oxygen pressure for the active-to-passive and passive-to-active transitions was not observed for SiC. This is due to the fact that both processes are controlled by SiC/SiO2 interfacial reactions. Studies were also conducted on active oxidation