In high-voltage devices such as thyristor, beveling is mostly used junction termination method to reduce the surface electric field far below the bulk electric field and to expand the depletion region thus that breakdown occurs in the bulk of the device rather than at the surface. However, coating material used to protect the surface of the device contain so many charges which affect the electrical characteristics of the device. And device reliability is also affected by this charge. Therefore, it is needed to analyze the effect of surface charge on electrical characteristics of the device. In this paper, we analyzed the breakdown voltage and leakage current characteristics of the thyristor as a function of the amount of surface charge density. Two dimensional process simulator ATHENA and two-dimensional device simulator ATLAS is used to analyze the surface charge effects.