PURPOSE: To restrain buried layers from rising and also accomplish an improvement in MOS character, an abatement of miniaturized element separation widths for bipolar elements, and a high-level integration of elements by making a portion of element formation areas at least and one side of buried layers at least facing to the foregoing portion of such areas contain a specific element having a given concentration.
CONSTITUTION: N + type buried layers 2 and P + type buried layers 3 are formed at P-type silicon substrate 1 which acts to be a support area. A ion implantation mask 4 is formed at portions corresponding to element separation areas as well as areas for forming bipolar elements and one kind of element ions 5 at least selected out of elements: i.e. oxygen, nitrogen, carbon, argon, neon, krypton, and helium is introduced by the ion implantation into the areas other than the portions corresponding to the element separation areas as well as the areas for forming bipolar elements. In such a case, implantation conditions shall be: (a) an accelerating voltage to be introduced into the faces in the vicinity of buried layers is desirable: (b) insulators are not formed at the implantation layers 6 and there is such a concentration that an excellent single crystal silicon is growable: (c) implantation doses amounting to 1×10 18 pc./cm -3 W5×10 22 pc./cm -3 are desirable.