We demonstrate remarkably rapid oxidation of (100) silicon at room temperature catalyzed by the presence of Cu3Si. Thermal oxidation of Si is normally carried out at temperatures above 700°C. Oxidation of many metal silicides occurs more rapidly than that of Si, but under controlled conditions results in a surface layer of SiO2. In contrast, the oxidation process described here produces a thick layer of SiO2 underneath the copper-rich surface layer. The SiO2 layer grows spontaneously to over 1 μm in thickness in several weeks in air at room temperature. Analysis by Rutherford backscattering, Auger electron spectroscopy, cross-sectional transmission electron microscopy, and scanning electron microscopy reveals the presence of Cu3Si at the buried SiO 2/Si interface, epitaxially related to the underlying Si substrate. Catalytic action by this silicide phase appears responsible for the unusual oxidation process.