PURPOSE: To prevent the generation of a punch-through and a reduction in a carrier mobility in an FET and to contrive the speedup of a semiconductor device by a method wherein a gate and gate electrode are formed on a semiconductor substrate and impurity ions are implanted in the substrate obliquely to the substrate from two directions toward a gate length from both sides of the gate electrode.

CONSTITUTION: A field insulating film 2 is formed on a P-type silicon (a P-type Si) substrate 1 and a gate insulating film 3 consisting of a silicon dioxide (SiO2) film and a gate electrode 4 consisting of a polysilicon film are formed. Then, an N-type well 5 is formed by implanting phosphorus ions (P+) in the substrate 1 from both sides of the gate electrode 4 to the direction of a gate length in such a way as to tilt the ions at -40° and +40° to the vertical surfaces. An impurity profile in the wall 5 subsequent to the implantation becomes a composed one of a real line to show the oblique implantation from the right of a gate and dotted lines to show the oblique implantation from the left of the gate. A source 6 and a drain 6 are formed by implanting boron difluoride ions (BF+2). An interlayer insulating film 7 and wirings 8 are formed and the formation of the significant part of an FET ends.