in a first embodiment of the present invention will be described with reference to fig1 in fig1 the power mosfet is fabricated from an n type substrate 1 having a top surface 1 a or main surface and a back surface 1 b which is opposite to the top surface 1 a the substrate 1 forms an n type first conduction type source region that is homogeneously doped with any of phosphorus p arsenic as and antimony sb which are n type impurities with a concentration ranging between 1 u00d7 10 18 and 1 u00d7 10 20 cm u2212 3 a trench 2 first trench is formed in the substrate 1 with a predetermined depth from the top surface 1 a the depth ranges for example between 1 and 100 micrometers a p type second conduction type base region 3 having a thickness ranging between 0 1 and 5 micrometers is formed in the trench 2 the base region 3 is homogeneously doped with b boron which is a p type impurity with a concentration ranging between 1 u00d7 10 15 and 1 u00d7 10 18 cm u2212 3 an n u2212 type first conduction type drift region 4 which has a predetermined thickness for.