Oxygen is the dominant impurity in pulled silicon. At 450 °C, thermal donors form in oxygen rich silicon. Using deep level transient spectroscopy, this donor is found to have an energy level of 0.142 eV below the conduction band at zero electric field, exhibiting behavior consistent with the Poole–Frenkel field assisted electron emission process. Using deep level transient spectroscopy in conjunction with calibrated uniaxial stress, we have determined the symmetry of the neutral 450 °C oxygen donor complex to beD2d. Possible models for the oxygen donor complex are presented which are consistent with the observed symmetry and with previous experiments.