Fast oxidation of amorphous (a)Si1−xGex:H by interfacial reaction withSnO2was observed at the temperature range of 400–500 °C. The rate of interfacial oxidation was very significant, while a test in a dryO2ambient at the same temperatures showed no oxidation ofSi1−xGex:H beyond the native oxide. The interfacial reaction of theSiGe:H/SnO2/glass system resulted in a layered structure of silicon oxide, tin oxide, and &bgr;‐Sn at theSiGe/SnO2interface. The extent of the interfacial reaction was found to depend on the Ge content in theSi1−xGex:H films; after annealing, the resultant silicon oxide layer is thicker for the Si‐rich SiGe layer than for the Ge‐rich composition. On the other hand, theSnO2layer was totally reduced by ana‐Ge:H top layer after a 1 h, 500 °C annealing procedure. ©1995 American Institute of Physics.