There is disclosed a simulation model for designing a semiconductor device, comprising adding at least a part of a difference between a density of a carrier described in a quasi-static manner with respect to a voltage applied between electrodes at a first time and a density of the carrier described in a transient state at a second time before the first time to the carrier density at the second time in accordance with a running delay of the carrier between both the times to thereby describe the carrier density at the first time in the transient state with respect to a semiconductor element having the first and second electrodes. A current flowing between the electrodes is described as a sum of a current flowing between the electrodes in the quasi-static manner, and a displacement current between the electrodes.