An integrated circuit device may include a substrate including a main surface, a compound semiconductor nanowire extending from the main surface in a first direction perpendicular to the main surface and including a first section and a second section alternately arranged in the first direction, a gate electrode covering the first section, and a gate dielectric layer between the first section and the gate electrode. The first section and the second section may have the same composition as each other and may have different crystal phases from each other.