A two-dimensional process simulation program has been developed. The process models used for this program are oxidation, diffusion, ion implantation, and deposition/etching of CVD films. The numerical models are based on a finite-difference approximation to diffusion equation. A large number of equations derived from the diffusion equation are solved by Stone's method because of its excellent rate of convergence. Attention is paid primarily to lateral impurity diffusion and lateral oxidation near the edge of the oxidation mask. Oxidation enhanced diffusion of boron is also included. We have obtained good quantitative agreement between calculated and experimentally observed diffused line capacitance variation with reverse bias voltage which is strongly affected by the lateral channel stop diffusion in a locally oxidized process.