PURPOSE: To obtain a desired high-voltage IC without damaging the characteristics of a element device to be used in a high-voltage IC, by a method wherein high impurity density buried layer is provided with a structure where the layer does not directly contact with a p-type semiconductor substrate.

CONSTITUTION: Formed is a first n-type epitaxial layer 11 whose resistivity is determined by the withstanding voltage required on a p-type semiconductor substrate 11. Then, an n-type buried layer 2 with a high impurity concentration is formed on a specified position within the epitaxial layer 11, and a second n-type epitaxial layer 3 is formed to bury the n-type buried layer 2. Then, an isolation area 4 is formed which extends to the p-type semiconductor substrate across the first n-type epitaxial layer 11 and the second n-type epitaxial layer 3. Then, a base region 5 and emitter region 6 for a transistor are formed on the island region that is formed by the isolation area 4, and an n-type collector-wall region 7 with a high impurity concentration is formed. Thus, it is possible to obtain a sufficient high withstanding voltage without making the resistivity of the buried layer 2 high.