A Czochralski silicon crystal was annealed at 1350degreesC to dissolve the vacancy-type grown-in defects. The faster dissolution rate of the grown-in defects was observed in the bulk of the silicon wafer than near the surface. This suggests that the presence of a higher concentration of silicon interstitials hinders the dissolution of the grown-in defects, which are composed of the vacancy clusters with the surrounding silicon oxide film. This expectation was confirmed by the observation that the dissolution rate of the grown-in defects near the surface of the silicon wafer in the oxygen atmosphere was slower than that in the argon atmosphere. This is in contrast with the previous argument that the presence of the excess silicon interstitials leads to a faster dissolution rate of vacancy-type defects.