Intrinsic point defects control the formation of grown-in defects in silicon crystals. Under stead?; state conditions, the type of the prevailing point defect species is exclusively determined by the ratio of pull rate and temperature gradient in the crystal at the interface. In this study, simulations have been performed for transient growing processes where the pulling rate has been abruptly changed. Large reservoirs of interstitials are formed in fast-grown. vacancy-rich crystals near the interface after abruptly reducing the pulling rate for 30 min. During further growth at high pull rate, these interstitial reservoirs are transformed into large ellipsoidal defect patterns. Experimental results are excellently reproduced if equilibrium concentrations are used as boundary conditions for interstitials and vacancies at all crystal surfaces.