A cold-wall rapid thermal processor is used for the wet oxidation of the commensurately grown GexSi1−x layers on Si substrates. The rate of oxidation of the GexSi1−x layer is found to be significantly higher than that of pure Si, and the oxidation rate increases with the increase in the Ge content in GexSi1−x layer. The oxidation rate of GexSi1−x appears to decrease with increasing oxidation time for the time-temperature cycles considered here. Employing high-frequency and quasi-static capacitance-voltage measurements, it is found that a fixed negative oxide charge density in the range of 1011– 1012/cm2 and the interface trap level density (in the mid-gap region) of about 1012/cm2 eV are present. Further, the density of this fixed interface charge at the SiO2/GeSi interface is found to increase with the Ge concentration in the commensurately grown GeSi layers.