Disclosed are a semiconductor device and a method of fabricating the same. The device may include a substrate, an active pattern in an upper portion of the substrate and is extending in a first direction, a gate electrode crossing the active pattern and extending in a second direction intersecting the first direction, a first gate spacer covering a side surface of the gate electrode, a first inhibition layer between the gate electrode and the first gate spacer, and a gate insulating layer between the gate electrode and the active pattern. The gate insulating layer may include a high-k dielectric layer and a gate oxide layer. The gate oxide layer may be between the high-k dielectric layer and the active pattern. The high-k dielectric layer may be between the gate oxide layer and the gate electrode.