Abstract: A semiconductor body (1 ) is provided having a first region (4) of one conductivity type adjacent one major surface (2). An insulating layer (5) is formed on the one major surface and masking means (6,7) are used to form over first and second areas (20 and 21) of the one major surface (2) windows (8,9,10) in the insulating layer (5) through which impurities are introduced to form a relatively highly doped region (11) of the opposite conductivity type adjacent the first area (20) and a relatively lowly doped region (12) of the opposite conductivity type adjacent the second area (21). The surface (5a) of the insulating layer (5) is exposed prior to introducing impurities of the one conductivity type for forming a region (13) within the relatively lowly doped region (12) of the opposite conductivity type and with a dose sufficient to form the region (13) but not sufficient to overdope the relatively highly doped region (11) so avoiding the need to mask the first area (20) during this step.