Method of fabricating of semiconductor device by forming two electrically insulated wells of the same type electroconductivity on semiconductor substrate

A fabrication method of a semiconductor device comprising the steps of:

• forming a first well of a first electroconductive type on one main surface of a semiconductor substrate of said first electroconductive type which is surrounded by a semiconductor layer of a second electroconductive type opposite to said first electroconductive type;
• forming a second well of said first electroconductive type of the main surface of said substrate which is electrically insulated from said first well and is electrically connected to said substrate;
• forming an electroconductive layer which connects said first well and said second well to each other on an insulator layer between said first and second wells;
• and
• partially removing said electroconductive layer to electrically insulate said first and second wells from each other after finishing a process which generates electric charges on the substrate;
• wherein said first well is used for an MOSFET constituting a memory cell and said second well is used for a peripheral circuit of said memory cell, and said electroconductive layer is connected to a gate electrode of said MOSFET.