The effects of high-concentration ozone gas (similar to 25%) exposure at atmospheric pressure with and without ultraviolet (UV) irradiation to a 4H-SiC(0001) surface has been investigated by X-ray photoelectron spectroscopy (XPS). The C 1s XPS spectrum for the 4H-SiC surface after standard RCA cleaning showed the appearance of a chemically shifted peak on the higher binding energy side of the SiC bulk peak. The chemically shifted peak was also observed even for the surface prepared by dipping a sample with sacrificed oxide film into 5% HF solution. Curve-fitting analysis using the Gaussian function revealed that the chemically shifted peak consisted of three components. The chemically shifted peak could be sufficiently eliminated using ozone exposure with UV irradiation. The cleaning mechanism of the 4H-SiC surface by ozone exposure is discussed, referring to the analysis of peak intensity for each component under different surface conditions corresponding to RCA cleaning and ozone exposure with and without W irradiation.