A MOSFET simulation method for calculating a characteristic value of a MOSFET to be simulated by first numerically calculating the electric potential, electron density, hole density, and mobility inside the MOSFET from simulation conditions including various parameters of the MOSFET, and then using the electric potential, electron density, hole density, and carrier mobility is provided. This method has the first step of calculating the carrier mobility .mu. using, of the simulation conditions, the impurity concentration N, temperature T, vertical electric field Ev, and substrate voltage Vb, from the equation .mu.(N, T, Ev, Vb)=.mu.0(N, T, Ev)+.mu.1(Vb), and the second step of calculating the electric potential .psi., electron density n, hole density p using the carrier mobility .mu. by solving the system of simultaneous equations made of a Poisson equation, the equation of continuity of electrons the equation of continuity of holes, the electron transport equation, the hole transport equation, for the electric potential, electron density, and hole density.