Semiconductor devices including active regions and gate electrodes are disclosed. An example semiconductor device according to the disclosure includes a gate electrode extending in a first direction, and first and second active regions extending in a second direction. The gate electrode has a side extending in the first direction. The first active region includes: a first center portion having a first width in the first direction; and a first end portion disposed at a first end of the first center portion, and having a second width in the first direction that is greater than the first width. The second active region includes: a second center portion having a third width in the first direction. The gate electrode overlaps along the side with portions of the first end portion and the second center portion.