Abstract: A method for the production of a semiconductor device comprises the steps of forming a stopper layer on a semiconducting substrate, forming a first opening part in the stopper layer thereby enabling the first opening part to establish an element separating area, etching the semiconducting substrate through the first opening part thereby forming a trench in the semiconducting substrate, partially etching the part of the stopper layer approximating closely to the trench thereby dilating the width of the first opening part, forming an oxide film on the stopper layer, in the first opening part, and inside the trench, removing the part of the oxide film rising above the stopper layer, removing the stopper layer, and contracting the lateral parts of the oxide film protruding from the trench.