A method of manufacturing an integrated circuit device includes forming a preliminary channel stack, which includes sacrificial layers and channel layers, on a substrate, forming a preliminary channel pattern and a fin-type active region by removing a portion of the preliminary channel stack and a portion of the substrate to define a buried trench, forming a sacrificial buried layer in the buried trench, forming a source/drain region on the fin-type active region, forming, on the sacrificial buried layer, a power via electrically connected to the source/drain region, removing a portion of the substrate to expose a bottom surface of the sacrificial buried layer, removing the sacrificial buried layer and forming, in the buried trench, a backside buried wiring layer connected to the power via, and forming a backside wiring structure electrically connected to the backside buried wiring layer.