A general theoretical approach to the modeling of several different process steps in fabrication of ion‐exchanged channel waveguides is presented. All of the commonly used fabrication processes are included, and the nature of the ion source and the effect of external electric voltage are taken into account. The model uses a numerical finite‐difference calculation of diffusion in the glass with boundary conditions and electrical current distribution chosen according to the process being modeled. A single computer program includes the model, and can be used for simulating a fabrication process with different successive process steps. Several calculated examples are given, all with experimentally obtained parameters for Ag+‐Na+exchange in Corning 0211 glass.