A hot carrier lifetime of a MOS transistor is estimated, depending on model formulas: 1/=1/0+1/b; b1sub-mbIdmb-2exp(a/|Vbs|), where denotes a lifetime, Isub denotes a substrate current, Id denotes a drain current, Vbs denotes a substrate voltage, 0 denotes a lifetime at the time the substrate voltage Vbs=0, b denotes a quantity representing deterioration of a lifetime at the time the substrate voltage |Vbs|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+Ageb; Ageb=1/Hb[IsubmbId2-m]exp(-a/|Vbs|)dt, where t denotes time, Hb is a model parameter, Age0 denotes a parameter representing a cumulative stress quantity at the time the substrate voltage Vbs=0, and Agebs denotes a quantity representing an increase of the cumulative stress quantity at the time the substrate voltage at |Vbs|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.

 
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