Semiconductor devices and methods of fabricating the same are provided. The method includes forming on a substrate an active pattern that protrudes from the substrate and extends in one direction; forming on the active pattern a sacrificial gate structure that extends in a direction intersecting the active pattern; forming on a side surface of the sacrificial gate structure a first spacer including a first portion at a lower level than a top surface of the active pattern and a second portion on the first portion, and reducing a thickness of the second portion of the first spacer.