Low temperature oxidation by microwave-discharged O-2 plasma has been investigated. The O2 plasma processing with a pressure of 100 mTorr at 200 degreesC shows 15 times faster oxidation rate than that of thermal oxidation in dry O-2 at 1150 degreesC. The spectrometry of the luminescence from the discharged plasma suggests that the ionized or highly excited neutral O radicals play an important role in the mechanism of the O-2 plasma-oxidation of SiC. The breakdown field strength of a 40 mn-thick plasma-oxide layer is estimated to be about 9.5 MV/cm.