An integrated circuit device includes, a first nano-sheet stack including a plurality of nano-sheets arranged on a fin-type active region extending in a first horizontal direction, a gate line extending in a second horizontal direction on the fin-type active region, a vertical structure contacting the plurality of nano-sheets, and a first gate dielectric layer disposed between the gate line and the plurality of nano-sheets and between the gate line and the vertical structure, wherein the gate line includes a first sub-gate portion disposed under each of the plurality of nano-sheets, the first gate dielectric layer includes a first portion disposed between the gate line and the plurality of nano-sheets, and a second portion disposed between the first sub-gate portion and the vertical structure, and a thickness of the second portion in the second horizontal direction is greater than a thickness of the first portion in the vertical direction.