To reduce the on-resistance in vertical power transistors, backside thinning is required after device processing. However, it is difficult to thin a SiC wafer with a high removal rate by conventional mechanical machining because its high hardness and brittleness cause cracking and chipping during thinning. In this study, we attempted to thin a 2-inch 4H-SiC wafer by plasma chemical vaporization machining (PCVM), which is plasma etching using atmospheric-pressure plasma. By controlling the scanning speed of the table and optimizing the oxygen percentage in the CF4+O2+He mixture gas, a maximum removal rate of 0.56 μm/min was obtained over the entire wafer. Furthermore, the surface roughness was improved after thinning. Therefore, PCVM can be used as an effective method for thinning SiC wafers.