Effect of nitrogen–oxygen (N–O) complexes on electrical properties of nitrogen‐rich Czochralski (CZ) silicon grown in a nitrogen atmosphere has been investigated during annealing in the temperature range from 650 to 1000 °C. Electrical and low temperature (8 K) Fourier transmission infrared spectrometer (FTIR) measurements point out that the carrier concentration of the nitrogen‐rich silicon varies with the annealing time and temperature, which is due to the formation and elimination of the N–O complexes acting as shallow thermal donors. After the N–O complexes are eliminated by annealing above 900 °C the carrier concentration of the nitrogen‐rich silicon is stabilized. It is suggested that the N–O complexes attract more oxygen atoms to form new electrically inactive N–O clusters, and lose their electrical activity.