A rigorous two-dimensional physical device simulator is developed to characterize the operation ofultra-small and highly doped semiconductor devices. To allow a better understanding ofthe device behavior, the physical phenomena which are taking place inside these devices are accurately modeled and included in the simulator. Implicit and explicit numerical schemes are applied to self-consistently solve the model equations and the effects ofboth schemes on the computational efficiency of the simulator are discussed. Finally, the obtained results from the simulator are compared with experimental characteristics ofa device with similar structure.