Abstract: In a semiconductor device including at least one active semiconductor region isolated by an oxide layer in a semiconductor substrate having a principal surface, at least two PN junctions, terminating at the oxide layer, are formed in the active region, by introduction of impurities into the active region with the active region surface never exposed during their formation. The junctions may partly reach the principal surface. The impurities may be introduced by ion implantation through a thin oxide film overlying the active region, and through use of other films placed on the oxide film, or by the known melt-through technique. At least one junction may be formed by epitaxial growth of a semiconductor layer of the opposite conductivity type.