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About 500-nm-thick films of Ge0.36Si0.64 and Ge0.28Si0.72 grown epitaxially on (100)Si have been oxidized at 700-degrees-C in wet ambient. A uniform GexSi1-xO2 oxide layer forms with a smooth interface between it and the unoxidized GexSi1-x layer below. The composition and structure of that layer remains unchanged as monitored by backscattering spectrometry or cross-sectional transmission electronic microscopy. The oxide of both samples grows as square root of oxidation duration. The parabolic rate constant increases with the Ge content and is larger than that for wet oxidation of pure Si at the same temperature. The absence of a regime of linear growth at this relatively low temperature indicates a much enhanced linear rate constant.