Preexisting oxidation stacking faults in silicon are expected to shrink when annealed in inert ambients. We have found that they sometimes exhibited a strange behavior of first shrinking and then expanding, though eventually shrinking again until disappearance. This phenomenon was not observed in silicon substrates with bare surfaces, or in oxygen‐free substrates. It was traced to the combined effect of oxygen precipitation and the action of certain surface coverings, silicon nitride films in particular. In a model to explain this phenomenon, the precipitation of bulk oxygen would generate excess silicon self‐interstitials which, when allowed to build up to some supersaturation, would feed the growth of the stacking faults. A bare surface would readily assimilate the excess self‐interstitials by means of surface regrowth, thus suppressing a supersaturation. Information concerning the supersaturation of self‐interstitials and the kinetics of surface regrowth, previously unavailable, has been obtained from this work.