The present invention provides a semiconductor device which includes trench-type element isolation which performs accurate alignment without deteriorating a device capability, and a method of manufacturing such a semiconductor device. Since a dummy gate electrode (14A) is formed in an edge proximity region of a trench (10A), a structure which does not create an etching remainder is realized. In addition, since a height difference is provided in a surface of the dummy gate electrode (14A) in such a manner that the height difference reflects a preliminary height difference between a surface of a silicon oxide films (2A) and a surface of a silicon substrate (1), it is possible to use the dummy gate electrode itself (14A) as an alignment mark.