Silicon self‐diffusion coefficients were determined by studying the diffusion of31Si into silicon crystals of various degrees of perfection and doping. For intrinsic silicon, the self‐diffusion coefficient can be represented byD=9,000 exp− (5.13 eV/kT) cm2/sec. Doping above intrinsic levels increases the diffusion coefficient. It it is assumed that silicon diffuses by means of vacancies, which act as acceptors, the influence ofn‐type doping can be attributed to the increase in total vacancy concentration caused by the excess electrons through a mass‐action principle. It is concluded that the vacancy mechanism is the most probable for silicon diffusion. The data of this investigation would indicate that the vacancy‐acceptor level is about 0.34 eV below the conduction band in silicon.