In this thesis, we use Poisson’s equation and continuity equations to design an equivalent circuit model for 2-D device simulation. The device simulation will be transformed into the circuit simulation. The simulation will become a mixed-level device and circuit simulation. We discuss the advantages and disadvantages between poly-Si gate and metal gate. And the simulation results of poly-Si gate will be compared with those of metal gate. Finally, the subject to be discussed is the non-Bernoulli equation for current expression. We will compare the Bernoulli method with non-Bernoulli method.