Abstract: A method for forming a guard zone (21) is disclosed, suitable for a guard ring for a Schottky barrier diode or for a channel guard zone for protecting the channel inversion layer of an insulated gate field effect transistor. The method uses anisotropic (straight-line) etching of a window in a thermally grown silicon dioxide layer (2) on a silicon body (1) combined with deposition of a metallic masking layer (4, 14), such as aluminum, which is subject to a shadow effect of reduced thickness at a sidewall (25) of the window. Slight etching of the metallic masking layer results in an aperture at the resulting edges of the masking layer located in the vicinity of the sidewall of the thermally grown oxide layer. Ions are then implanted with the body through the aperture, to form the guard zone (21).