High‐resolution, rapid synchrotron x‐ray topography is used to study oxygen‐induced microdefects and their spatial distribution in a large number of (100)n‐type silicon wafers, which had undergone different two‐stage thermal anneals. Section topographs reveal a 40–60‐&mgr;m‐thick defect‐free zone on the surface of a wafer annealed first at 800 °C for 20 h and then at 1150 °C for 4 h.