Suppression of oxidation‐stacking‐fault (OSF) generation is studied by x‐ray section topography, etching technique, and transmission electron microscopy (TEM). Microdefects (MD’s) are generated in bulk Si during N2atmosphere annealing at about 1000–1100 °C, and their generation is confined to the inner part of the Si wafer. These MD’s grow rapidly during subsequent oxidation. The grown MD’s contribute to stacking faults (SF’s) in the inner part of bulk Si. On the contrary, surface OSF’s are not introduced by the subsequent oxidation because no MD’s are generated in the surface layer by the preannealing. The suppression effect of OSF generation by N2atmosphere preannealing is demonstrated using several samples.