vanadium cr chromium ni nickel or the like is adopted it is necessary to make an impurity concentration in the silicon substrate 1 more than 5 u00d7 10 18 cm u2212 3 preferably more than 7 u00d7 10 18 cm u2212 3 so as to make an ohmic contact with the electrode material the barrier height u03c6 b of the electrode material for silicon is 0 4 0 6 ev as shown in fig8 if the impurity concentration is more than 5 u00d7 10 18 cm 31 3 the contact resistance between the electrode material and the silicon substrate 1 begins to rapidly be reduced and if the impurity concentration is more than 7 u00d7 10 18 cm u2212 3 the contact resistance becomes less than 10 u2212 3 u03c9 u00b7 cm 2 0048 fig9 shows a relationship between v ds voltage between the source and the drain and i ds current between the source and drain of this power mos fet voltage of the gate v g is a parameter shown in figure as being used as an index so as to judge whether the contact is a schottky contact 0049 fig1 shows a relationship between this calculated v f and a concentration of as in the silicon substrate 1 as.