Rapid thermal annealing (RTA) can be applied to dissolve small defects such as voids or small-sized oxygen precipitates and to manipulate vacancies in a specific depth from the surface. This can be achieved at elevated temperatures around 1300 C and via NH 3 dissociation at the surface at temperatures >1150 C. In an earlier study (Araki et al., 2013), it had been demonstrated already that even under oxidizing ambient, enhanced bulk micro defects formation around 1300-1350 C can occur. The near-surface region is monitored via its homogeneity of precipitation and in-depth vacancy profiling by Pt-diffusion. Simulations of defect dissolution during RTA processes are performed up to 1290 C under different ambient. The size-dependent defect dissolution behavior is predicted and verified by measurement of the gate oxide integrity.