The diffusivity of phosphorus is measured in silicon with nearly uniform arsenic or boron background dopingno>(0.1<n/ni<30) at temperatures of 915, 1015, and 1105 °C. It is found that diffusion via neutral and single negatively charged point defects are sufficient to account for the experimental data, with no need to include diffusion via double negatively charged point defects. Greatly reduced diffusivity is observed in the boron‐doped samples, which is consistent with the formation of immobile donor–acceptor pairs. Activated diffusion and pairing coefficients are calculated based on this work and combined with experimental results previously reported in the literature. ©1995 American Institute of Physics.