An integrated circuit device is provided. The device includes: lower source/drain areas; lower contacts respectively on bottom surfaces of the lower source/drain areas; upper source/drain areas spaced apart from the lower source/drain areas in a vertical direction; upper contacts respectively on upper surfaces of the upper source/drain areas; and a first vertical conductive rail electrically connected to a first contact of the lower contacts and the upper contacts, the first vertical conductive rail extending in the vertical direction, and including a first portion having a first upper surface at a first vertical level and a second portion having a second upper surface at a second vertical level lower than the first vertical level. The second portion overlaps a first upper contact among the upper contacts in the vertical direction.