The rate and concentration of thermal donors generated during 450°C anneals were observed to be dependent on wafer thermal history. Oxygen thermal donors formed by the silicon-vacancy and silicon interstitial models were examined and the silicon-interstitial donor formation was observed to be the dominating mechanism for the 450°C oxygen thermal donor. Thermally induced microdefects were also observed. Depending on the wafer thermal history less than 1 × 10¹⁴ donors/cm³ to as much as 3.7 × 10¹⁴ donors/cm³ were formed during the 450°C anneals.