Fabrication method of a semiconductor device

A fabrication method of a semiconductor device, comprising:

• forming an electrode on a substrate having a main surface;
• forming a predetermined semiconductor layer on said substrate;
• forming an insulation film on said substrate between said step of forming an electrode and said step of forming a semiconductor layer;
• forming a first mask material so as to cross said semiconductor layer;
• introducing impurity ions of a predetermined conductivity type into said semiconductor layer using said first mask material as a mask to form a pair of first impurity regions having a predetermined impurity concentration at a portion of said semiconductor layer located at one region and another region with said mask material therebetween, a portion of said semiconductor layer located right under said mask material being a channel region;
• forming on said semiconductor layer a second mask material covering said channel region entirely and respective portions of said first impurity regions constituting a pair;
• and
• introducing impurity ions of a predetermined conductivity type into said semiconductor layer using said second mask material as a mask to form a pair of second impurity regions having an impurity concentration higher than said predetermined impurity concentration at a portion of said first impurity regions located at one side and another side with said channel region therebetween, wherein
• in said step of forming an electrode, said electrode has one side and another side opposite to each other, and all of said channel region and respective portions of said one pair of first impurity regions are formed overlapping with and facing said electrode;
• and
• a distance starting from a first region where a plane including said one side of said electrode intersects one of said first impurity regions up to a side of said channel region closest to the first region is set shorter than a distance starting from a second region where a plane including said another side of said electrode intersects the other of said first impurity regions up to a side of said channel region closest to the second region.