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 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 .