Plasma hydrogenation of Czochralski Si has been performed to investigate the introduction of Si–O stretch modes and their correlation with thermal donor formation. Plasma hydrogenation at 275 °C introduces a well‐resolved vibrational absorption band at 1005 cm−1, while absorption due to electronic excitations for thermal donors remains weak. We attribute this band to a Si–O precursor center for thermal donor formation, and suggest it is the oxygen dimer center discussed in other studies of oxygen in Si. Vibrational modes introduced at 990 and 1000 cm−1during post‐hydrogenation furnace annealing at 400 °C correlate with thermal donors TD2 and TD3, respectively. Stretch frequencies for Si–O in thermal donor centers are compared to those for oxygen aggregates in oxygen‐implanted and electron‐irradiated Si.