A model for arsenic diffusion in silicon is proposed based on Hu’s theory which takes into account the degeneracy of the mobile carriers, partial ionization of the impurity atoms, single acceptor level vacancies, and the internal electric field. For a constant source diffusion, the transport equation describing the As+‐V−system can be separated. An efficient computer program based on a quasilinearization technique is written to obtain the impurity profiles from the processing data. It is shown that partial ionization significantly affects the diffusion process at high concentrations. The use of classical statistics yields an underestimate of the impurity concentration values. The computed profiles strongly depend on the values used for the intrinsic diffusion coefficient and vacancy energy. There is very good agreement between the vacancy‐aided model and experimental results reported by Chiu and Ghosh using neutron activation analysis.