Lateral diffusion enhancement of boron and phosphorus by excess point defects, excess interstitials during thermal oxidation of silicon and excess vacancies during high concentration phosphorus predeposition, has been investigated experimentally and numerically. Two-dimensional steady state excess point defect concentration profiles were obtained by a finite difference method. Numerical result was compared with the experimental data and the values of excess point defect recombination velocity (S) at the unoxidizing Si-SiO² interface divided by the point defect bulk diffusivity (D), S/D, were found out to be about 0.7/μm for excess interstitials and about 1.3/μm for excess vacancies.