Surface reactions of the 6H-SiC(0001) 3×3 with oxygen molecules (O₂) at high temperature were investigated using reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). The Si-terminated 3x3 surface transformed into the C-rich 1×1 surface by O₂ exposure of 1.2×10⁵L at 1000°C. Mass spectra measured during the experiment using a Quadrupole Mass Spectrometer (QMS) suggest that Si atoms and C atoms on the 3×3 surface were etched by the O₂ exposure. Morphologies of the 3×3 surfaces before and after the O₂ exposure were also observed using scanning electron microscopy (SEM). Many droplets were found on the 3×3 surface, which were determined to be Si droplets generated in the preparation process of the 3×3 phase. The Si droplets were removed from the surface by the O₂ exposure at high temperature.