An Insulated Gate Field Effect Transistor (IGFET), fabricated using Shallow Trench Isolation (STI), has an edge of a channel region of the IGFET which has a curved shape with a controlled radius of curvature so as to reduce the electric field at the edge of the channel region. A method of controlling the shape of the edge of the channel region is to limit the supply of oxygen to the region at the edge of the channel region during the oxidation process when the side walls of the silicon island, in which the transistor will be formed, are initially covered with a layer of silicon oxide.