The initial oxidation of the C-terminated 3C-SiC(100) c(2x2) surface is investigated by synchrotron radiation-based core level photoemission spectroscopy at the Si 2p and C 1s core levels. Contrary to Si-rich SiC surfaces, the C-terminated one is found to be much less reactive to oxygen with much higher exposures and temperatures required to grow similar amount of oxides. The latter include predominantly mixed Si-O-C oxides with a non-abrupt oxide/SiC interface. The lack of dangling bonds on the surface, CO/CO2 formation and C plane limiting oxygen atoms insertion into the SiC lattice are likely at the origin of this behavior.