The microscopic nature of the degradation of oxide layers in Si/SiO2/Si structures induced by annealing in the temperature range 1200–1320 °C in inert or weakly oxidizing atmospheres has been studied. Electron‐spin‐resonance measurements have been performed on unannealed and annealed samples subsequently subjected to &ggr; orXradiation or hole injection. Two oxygen‐vacancy‐related defect centers were observed, the monovacancyE&ggr;’center and the multiple vacancyE&dgr;’—both were observed in substantially larger numbers in annealed oxides as compared to unannealed oxides. Etchback profiling of the paramagnetic defect distributions shows that they are distributed nonuniformly throughout the annealed oxides with the highest densities close to the two Si/SiO2interfaces. Electrical measurements of fixed oxide charge induced byXirradiation indicate that annealing results in the creation of both positive and negative charge traps. The numbers of positive trapped charges and their radiation dose dependence are inconsistent with their origin being identified simply with the paramagnetic oxygen‐vacancy centers. Infrared measurements of the O interstitial content of the float‐zone Si substrates of annealed and unannealed samples reveal that the interstitial concentration increases as a function of anneal temperature/time. Atomic force microscopy measurements reveal that the SiO2/Si substrate interfaces are roughened during high‐temperature annealing. The data are interpreted in terms of a model in which oxygen is gettered from the oxide film into the over‐ and underlying Si. The O are incorporated into the Si as interstitials and it is their solubility limit at the anneal temperature which drives the gettering process. The oxygen‐vacancy defect profiles near to both Si/SiO2interfaces are not well predicted by the gettering model suggesting that other interface‐related defect creation processes may be active. ©1995 American Institute of Physics.