In a reliable semiconductor device and a method of fabricating the semiconductor device, a difference in height between upper surfaces of a cell region and a peripheral region (also referred to as a level difference) is minimized by optimizing dummy gate parts. The semiconductor device includes a semiconductor substrate including a cell region and a peripheral region surrounding the cell region, a plurality of dummy active regions surrounded by a device isolating region and formed apart from each other, and a plurality of dummy gate parts formed on the dummy active regions and on the device isolating regions located between the dummy active regions, wherein each of the dummy gate parts covers two or more of the dummy active regions.