In this paper, through the investigation of the effect of rapid thermal processing (RTP) at different temperatures on oxygen precipitation in Czochralski (CZ) silicon wafers subjected to two-step (low–high) anneal and one-step high-temperature anneal, the enhancement role played by vacancies in oxygen precipitation occurring at low temperature and high temperature have been revealed. For the two-step anneal, the RTP-introduced vacancies significantly facilitate the formation of oxygen precipitate nuclei during the low-temperature anneal and, therefore, enhance oxygen precipitation during the subsequent high-temperature anneal. Regarding the one-step high-temperature anneal, the RTP-induced vacancies that later combine with oxygen atoms to become the O₂V species significantly enhance the early stage oxygen precipitation in terms of the precipitation rate, however, the RTP-induced vacancies do not increase the amount of precipitated oxygen atoms in the CZ silicon wafer subjected to a prolonged high-temperature anneal. Due to the fact that for the CZ wafer with prior RTP the one-step high-temperature anneal produces much lower density bulk microdefects than the two-step (low–high) anneal, it is believed that the low-temperature anneal is a must for the 'magic denuded zone' process.