Infrared spectroscopy has been applied to the study of the kinetics of oxidation in high‐pressure dc‐sputtered amorphous silicon. The different spectra obtained during the evolution of the oxidation are processed by factor analysis. Two oxidation mechanisms have been found. Their associated infrared spectra and time evolution can be explained by a model that proposes the existence of a two‐level microstructure. The spectra associated with each one of the oxidation mechanisms seems to correspond mainly to SiO2, modified by the presence of surface modes.