A transistor device includes an active region surrounded by an isolation structure, a gate structure disposed over the active region and the isolation structure, and a source/drain disposed in the active region. The gate structure includes a body portion extending in a first direction, a head portion extending in a second direction, and a pair of wing portions disposed at two opposite sides of the body portion. The first direction and the second direction are perpendicular to each other. Each of the wing portions is in contact with the head portion and the body portion.