Electron cyclotron resonance (ECR) plasma oxidation of SiGe alloys was investigated at temperatures from room temperature to 500°C. Both Si and Ge are shown to be fully oxidized, forming SiO 2 and GeO 2 . Auger depth profiling reveals that there is no Ge-rich SiGe layer after oxidation. With increasing temperature up to 500°C, the oxide is stoichiometric and it does not lose its GeO 2 component. Oxidation has also been carried out at both positive and negative sample bias in order to identify the role of ions, electrons, and neutrals. From biasing experiments negative oxygen ions and atomic neutrals appear to be the major reaction species.