To provide a paired parameter which can give a calculating result corresponding to a real measuring value over a wide range of dose value during ion implantation or of temperature during annealing process in a simulation method which searches a density distribution after the annealing process of impurities which is made ion implantation in a semiconductor substrate.

When a density distribution of As which is made ion implantation in a silicon substrate via a silicon oxide film after annealing process is searched, a calculating result which properly corresponds to real measured data can be obtained by fixing Dm (As).f and Dn (As).f which are products of a diffusion constant Dm (As) of a pair of As and interstitial silicon, a diffusion constant Dn (As) of a pair of As and positive hole and a parameter f of '+1' model which controls generation of point failure at a predetermined value and by fixing a diffusion constant D (As) of As in a silicon oxide film and a segregation coefficient m (As) at predetermined values.