We investigate the initial interface formation of oxide/C-terminated beta-SiC(100) c(2 x 2) and oxide/C-rich beta-SiC(100) 1 x 1 surfaces by Si 2p and C 1s core level photoemission spectroscopy using synchrotron radiation. Contrary to the Si-rich SiC surfaces, the C-terminated and C-rich surfaces are much less reactive to oxygen, with much higher exposures and temperatures required to grow a significant amount. of oxides. This leads to nonabrupt oxide/SiC interface formation including predominantly mixed oxide products containing carbon species, with marginal amounts of SiO2 only. The lack of dangling bonds on the surface together with the C plane and/or graphitic species limiting oxygen insertion into the SiC lattice are likely at the origin of this very different behavior when compared to Si-rich SiC surfaces. (C) 2004 American Vacuum Society.