A semiconductor device of high reliability and element-integrating performance, has a substrate (silicon substrate), a first trench made in the silicon substrate, a passive element layer buried in the first trench, and a first insulating film (silicon nitride film) arranged between the first trench and the passive element layer. The passive element layer projects upwardly relative to the substrate, and so too preferably the adjacent insulating film. An active element is formed such that its gate electrode, which is preferably fully silicided, has an upper end at a level higher than the upper surface of the passive element film.