Detailed distributions of diffusion of phosphorus into silicon have been measured by the four-point probe method. During the measurement, each successive layer is removed by the anodic oxidation technique. These impurity distributions are found to deviate from the error function complement even with the surface concentration kept constant during diffusion. If it is assumed that this is due to a concentration denpendence of the diffusion coefficient, the experimental results would indicate that the diffusion coefficient rises very rapidly when the concentration exceeds 1019/cm3.Detailed distributions of diffusion of phosphorus into silicon through silicon dioxide films of different thicknesses grown by thermal oxidation have also been measured by the method described above. The experimental data indicate that the silicon dioxide films remain effective for masking at a diffusion temperature as high as Td = 1300℃. With diffusion time close to masking failure time, the surface concentration is found to be close to l017/cm3 and the diffusion depth is found to be very small (～1 μ). However, for sufficiently long diffusion times, the surface concentrations apparently reach an ultimate value not influenced by the thickness of the oxide film, it remains a constant as long as the vapour pressure of diffusont source is kept constant. Detailed distributions of diffusion of phosphorus through a silicon dioxide film are also found to be strongly dependent on the nature and the condition of the diffusing source. An increase of the thickness of the oxide film during diffusion has been observed; it might affect the impurity distribution especially in the region near the surface.