A method of manufacturing a semiconductor device includes introducing at least a first and a second trench pattern including array trenches from a first surface into a semiconductor substrate, wherein an array isolation portion of the semiconductor substrate separates the first and second trench patterns. A buried gate electrode structure is provided in the first and second trench patterns at a distance to the first surface. In a single etch process, both a device separation trench having a first width is introduced into the array isolation portion and cell separation trenches having at most a second width that is smaller than the first width are introduced into semiconductor fins between the array trenches. Switching devices integrated in the same semiconductor die may be formed in a cost effective way.