Anodic oxides of SixGe1−x (0 ≤ x ≤ 1 ) alloys have been made by plasma assisted oxidation in a microwave frequency (2.45 GHz) reactor working in the constant current bias mode. Oxide films ∼15 – 40 nm (depending upon the Ge concentration) were obtained in 10 minutes without a temperature rise of the substrate of more than 100 °C. Detailed infrared absorption studies of the oxides enabled the Si-O-Si, Ge-O-Ge and Si-O-Ge vibrational modes to be identified, the strongest being at 1056, 858 and 1000 cm−1 respectively. These modes are associated with the O asymmetric stretch, their values are at lower wavenumbers than in bulk oxides due partly to ultraviolet radiation induced structural modification and partly to thin film optic effects. A statistical model for the different bonds present in SixGe1−xO2, when used to simulate the infrared spectrum does not predict the experimentally observed form, the Ge-O-Ge peak is in general too intense in the experimental spectrum. Auger electron spectroscopy profiling of the SixGe1−x oxides suggests that there is a build-up of Ge close to the surface/oxide interface so that when combined with the infrared data, we conclude that there is a GeO2 rich region at the surface/oxide interface. The oxide is, however, globally stoichiometric. Electrical measurements (C(V) and interface state density) were begun on metal-oxide-semiconductor (MOS) capacitors for Si1−xGex. oxides over the range of concentrations 0 ≤ x ≤ 1. Only Si1−xGex oxides with x≤0.15 appear to yield satisfactory MOS capacitor curves.