A hot carrier lifetime of a MOS transistor is estimated, depending on model formulas: 1/=1/₀+1/_b; _b1_sub^-mbI_d^mb-2exp(a/|V_bs|), where denotes a lifetime, I_sub denotes a substrate current, I_d denotes a drain current, V_bs denotes a substrate voltage, ₀ denotes a lifetime at the time the substrate voltage V_bs=0, _b denotes a quantity representing deterioration of a lifetime at the time the substrate voltage |V_bs|0, and mb and 'a' are model parameters. Furthermore, a parameter Age representing a cumulative stress quantity is calculated depending on model formulas: Age=Age₀+Age_b; Age_b=1/H_b[I_sub^mbI_d^2-m]exp(-a/|V_bs|)dt, where t denotes time, H_b is a model parameter, Age₀ denotes a parameter representing a cumulative stress quantity at the time the substrate voltage V_bs=0, and Age_bs denotes a quantity representing an increase of the cumulative stress quantity at the time the substrate voltage at |V_bs|0. Thereby, a lifetime in actual use is determined with accuracy even when a substrate voltage is applied, and circuit characteristic degradation is simulated with high accuracy.