Initial oxidation of the SiC (0001) (root3xroot3)-R30degrees and 3x3 surfaces at various temperatures is studied by using Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). The results show that the 3x3 surface oxidizes with maintaining its original periodicity, while the root3xroot3 surface changes into a 1x1 structure. Moreover, the root3xroot3 surface loses almost all Si-Si bonds by a low oxygen exposure, in contrast the 3x3 surface does not. There is no significant difference among the Auger spectra at different sample temperatures in the case of the root3xroot3 surface, while thermal activation is found in the 3x3 case at 500degreesC.