Semiconductor device and method of fabricating the same

A semiconductor device includes: a first active pattern extended in a first direction on a substrate; a second active pattern extended in the first direction and spaced apart from the first active pattern in a second direction on the substrate; a field insulating layer between the first active pattern and the second active pattern on the substrate; a first gate electrode on the first active pattern; a second gate electrode on the second active pattern; and a gate isolation structure separating the first gate electrode and the second gate electrode from each other on the field insulating layer, wherein a width of the gate isolation structure in the second direction varies in a downward direction from the upper isolation pattern.