The gate-all-around (GAA) type semiconductor device may include source/drain layers, a nanowire channel, a gate electrode and an insulation layer pattern. The source/drain layers may be disposed at a distance in a first direction on a semiconductor substrate. The nanowire channel may connect the source/drain layers. The gate electrode may extend in a second direction substantially perpendicular to the first direction. The gate electrode may have a height in a third direction substantially perpendicular to the first and second directions and may partially surround the nanowire channel. The insulation layer pattern may be formed between and around the source/drain layers on the semiconductor substrate and may cover the nanowire channel and a portion of the gate electrode. Thus, a size of the gate electrode may be reduced, and/or a gate induced drain leakage (GIDL) and/or a gate leakage current may be reduced.