This work describes the characterization of defect centers in 3C-SiC, 4H-SiC, and 6H-SiC. The different SiC crystal structures are examined with electron paramagnetic resonance after thermal oxidation, and after dry (<1 ppm H2O) N2 or O2 heat treatment. The centers are described by g values that range from 2.0025 to 2.0029, which are typical of C dangling bonds. Because the centers are activated in ambients that eliminate H2O and are passivated in ambients that contain H2O, it is suggested that the centers are C dangling bonds created during the dry heat treatment when hydrogen or a hydrogenous species releases from C bonds. The activation characteristics for the centers is the same for both 6H and 3C polytypes; however, centers in the 6H-SiC samples are passivated at lower temperatures than the centers in the 3C-SiC samples. The passivation behavior is attributed to differences in the hydrogen diffusion rates in these materials rather than significant differences in the chemistry of the centers. Etching studies conducted with hydrofluoric acid indicate that the centers are not located in the SiO2, but are located in the SiC at a distance of, at most, 200 nm from the SiO2/SiC interface. © 2000 American Institute of Physics.