The stability of an amorphous GexSi1−xO2in contact with an epitaxial (100)GexSi1−xlayer obtained by partially oxidizing an epitaxial GexSi1−xlayer on a (100)Si substrate in a wet ambient at 700 °C is investigated forx=0.28 and 0.36 upon annealing in vacuum at 900 °C for 3 h, aging in air at room temperature for 5 months, and immersion in water. After annealing at 900 °C, the oxide remains amorphous and the amount of GeO2in the oxide stays constant, but some small crystalline precipitates with a lattice constant similar to that of the underlying GeSi layer emerge in the oxide very near the interface for bothx. Similar precipitates are also observed after aging for bothx. The appearance of these precipitates can be explained by the thermodynamic instability of GexSi1−xO2in contact with GexSi1−x. In water at RT, 90% of GeO2in the oxide is dissolved forx=0.36, while the oxide remains conserved forx=0.28.