Double Injection(DI) switching devices consist of PS0+T and nS0+T contact separated by a nearly intrinsic semiconductor region containing deep trap. The equation set for DI switching device simulation by FEM is proposed. The existance of deep trap requires the modification of conventional equation set. So recombination rate equation is modified and a new equation is included in the equation set which conventionally consists op Poisson equation and current continuity equation. Consequently, the modeling equation set, which is proposed in this paper, can be applied to other semiconductor devices with trap.