The oxidation behavior of a strained SiGe epitaxial layer on silicon substrate in both dry and wet ambient was investigated. We found that the oxide thickness at which oxidation saturation occurs increases with oxidation temperature and is larger for wet oxidation than dry oxidation at the same temperature, although Ge concentration at the oxidizing interface is much higher for wet oxidation. This observation shows that the oxidation saturation is not due to the thin, higher Ge-concentration layer at the oxidizing interface or the remaining strain of SiGe layer as reported previously. Different from the monotonous increase with oxidation time for the SiGe layer oxidized in dry oxygen, the degree of strain relaxation in the SiGe layer increases up to about 90% in a short time and then decreases slowly during wet oxidation at 1000 degrees C. These results suggest that the expansion in volume due to the transformation of SiGe to oxide greatly contributes to the anomalous strain relaxation process for fast oxidation in wet ambient. In addition, higher density of threading dislocations was observed in the samples oxidized in wet ambient. (c) 2008 The Electrochemical Society.