Secondary ion mass spectroscopy (SIMS) and Fourier transform infrared (FTIR) absorption have been studied in thin oxides ofSi1−xGexgrown by plasma oxidation. SIMS analysis reveals that Ge can migrate to the oxide film surface leaving the oxide in the SiGe interface region Ge-depleted. This is in contrast to thermally grown oxides. Water selectively attacks the Ge-rich part of the oxide. In the FTIR spectra of the SiGe oxides, specific peaks identified with the vibration of O in Si–O–Ge and Ge–O–Ge bonds have been observed for the first time. These latter observations confirm that for the plasma oxidized films, the Ge is chemically bonded in the oxide network. ©1998 American Institute of Physics.