The morphology of surface reactions for Au/SiO2/Si structures has been studied as a function of environment. It was found that the reaction between thin gold film dots and thermally oxidized Si was strongly influenced by the partial pressure of oxygen. When samples are held at elevated temperatures (above 500 °C) in the dynamic vacuum, an apparent decomposition of the oxide film with subsequent migration of Au along the exposed silicon surface was observed. The migration was found to follow the crystallographic directions of the silicon. Reduction of the oxide was dependent on the presence of the Au layer as regions free of Au remained intact. The reaction as a function of time, temperature, SiO2 thickness, and ambient conditions has been studied using optical microscopy as well as electron microprobe, microscopy, and diffraction techniques.