An integrated circuit device includes a fin-type active region that extends from a substrate and in a first lateral direction, a device isolation film on a trench region on the substrate, an insulating liner structure that extends through the substrate in a vertical direction and contacts the device isolation film at a first vertical level, a via power rail that extends through the device isolation film in the vertical direction and comprising a first bottom surface at a second vertical level, and a backside power rail comprising a main rail and a protrusion rail, where the main rail extends through the substrate and the insulating liner structure in the vertical direction, and where the protrusion rail extends from the main rail toward the via power rail.