Dependence of mechanical strength of Czochralski silicon (CZ-Si) wafers on the temperature of oxygen precipitation annealing has been studied both experimentally and theoretically. Thermal stress was applied to CZ-Si wafers after oxygen precipitation annealing at 1100 degrees C or 1000 degrees C after preannealing at 800 degrees C. The warpages and the densities of slip dislocations in the wafers annealed at 1100 degrees C are much higher than those in the wafers annealed at 1000 degrees C, nevertheless each precipitate density is almost equal. Transmission electron microscopy observations of the 1100 degrees C samples showed that both platelet and polyhedral precipitates were generated, but very few of these precipitates actually generated punched-out dislocations. In contrast, in the 1000 degrees C samples, only platelet precipitates were generated, many of which generated punched-out dislocations. Further studies showed that slip dislocations formed only from platelets which did not punch out dislocations, i.e., slip dislocations formed only in the 1100 degrees C samples. The mechanism of the generation of slip dislocation by oxide precipitates is discussed With calculated results of the system energy change due to slip dislocation generation.