The precipitation kinetics of oxygen and the evolution of the precipitate density in preannealed CZ silicon wafers was studied in the temperature range between 950° and 1150°C. It is shown that the number of oxygen nuclei that were created during a 700° or 800°C preanneal decreases exponentially with increasing process temperature. The density of oxygen precipitates in the bulk of the wafer decreases at high temperatures by an empirically determined activation energy of 3.15 eV.