Ce has been introduced into single crystal Si by means of vacuum deposition of Ce onto Si wafer, and then annealing at 1050℃ for 20 hours in vacuum.In the annealing process, Ce-Si alloy was formed on the surface at first, and then the Ce atorms diffused into Si and produced a diffusion region of Ce with thickness about 4.5 μm. The concentration profile of Ce was determined by SIMS. The diffusion coefficient of Ce in Si at 1050℃ was obtained as 3.9×10-13 cm2/s. The average resistivity ρ of the Ce diffusion layer was measured from 77K to 450K.