A systematic Fourier‐transformed infrared‐spectroscopy study of oxygen and carbon in isolated form and as complexes in the silicon lattice has revealed a direct correlation between the decrease of substitutional carbon concentration and the decrease of interstitial oxygen concentration during 750 °C annealing. At a concentration exceeding 2 ppma, carbon was also found to enhance oxide precipitate growth. After completing a three‐step annealing (1100 °C+750 °C+1000 °C), an oxide‐precipitate‐related IR‐absorption band was observed. The changes of the IR‐absorption band were correlated with annealing‐induced changes in the state of carbon. A direct incorporation of carbon into oxide precipitates, and/or carbon interaction with silicon self‐interstitials generated during oxygen precipitation, are suggested to have an effect on reducing lattice strain associated with the oxygen‐precipitation process.