The reduction of SiO2by Al was studied in Al/SiO2/Si structures above 350 °C. It was found that Al displaces Si in the oxide, forming an Al–O compound with an Al:O concentration ratio between 1:1 and 1.3:1. In the reacted areas, less than 1 at. % Si is left in what was originally a pure SiO2matrix. The activation energy for the reaction in a pyrogenic oxide is approximately 2 eV. The reaction was found to be responsible for electrical failure of diodes manufactured using Al/SiO2/Si technology. ©1996 American Institute of Physics.