A method of manufacturing a semiconductor device, comprising the steps of sequentially forming a buried region and an epitaxial layer on a major surface of a semiconductor substrate, forming a conductive layer along an annular trench extending to the buried region, filling the annular trench with an insulating material and forming a functional element in said epitaxial layer surrounded by said buried region and said insulating material within said annular trench. In this method, the step of forming the conductive layer along the annular trench is carried out by the steps of forming an annular trench extending through said buried region, and depositing a conductive layer on only a side wall surface of said annular trench.