Method of forming a semiconductor device which prevents field concentration

In a semiconductor device comprising a first conductivity type semiconductor substrate, a second conductivity type first semiconductor region formed on said semiconductor substrate through p-n junction isolation, and a conductive layer extending above said first semiconductor region across an end portion of said first semiconductor region, a method of forming a structure for preventing field concentration caused in said end portion of said first semiconductor region, existing under said conductive layer, through influence exerted by an electric field from said conductive layer, comprising the steps of:

• forming a first insulating film on said end portion of said first semiconductor region;
• forming at least one conductive plate on said first insulating film;
• introducing an impurity into said first semiconductor region by using said conductive plate as a mask to form at least one first conductivity type second semiconductor region being alternately arranged with said conductive plate so that end portions of said conductive plate and said second semiconductor region overlap with each other, in a surface of said end portion of said first semiconductor region;
• and
• forming a second insulating film over said first insulating film and said conductive plate, wherein
• said conductive layer is formed on said second insulating film.