Oxygen content in the bulk of Czochralski silicon was analyzed by using micro‐Fourier transform infrared spectroscopy in a transversal wafer cross‐section configuration. This technique locally distinguishes between interstitial oxygen and oxygen precipitates in wafers used as substrates for epitaxial layer growth. Systematic measurements performed in the 5000–700 cm−1wavenumber range clearly indicate the presence of oxygen microprecipitates in the bulk of the processed silicon wafers. Quantitative determination of oxygen precipitate density is reported and compared with the measured interstitial oxygen concentration.