An integrated circuit device includes a device isolation trench defining an active area, a gate trench extending in a first direction across the active area and the device isolation film, a gate dielectric film covering an inner wall of the gate trench, and a conductive line filling a part of the gate trench above the gate dielectric film. The active area includes a fin body portion located under the conductive line, and a thinner fin portion protruding from the fin body portion toward the conductive line and having a width less than a width of the fin body portion in the first direction.