Provided is a compound semiconductor device. The compound semiconductor device according to embodiments of the inventive concept includes a first semiconductor layer having a fin extending in a first direction on a substrate, an upper gate electrode extending in a second direction perpendicular to the first direction on the first semiconductor layer, a second semiconductor layer disposed between a sidewall of the fin and the upper gate electrode, a dielectric layer disposed between a top surface of the fin and the upper gate electrode, and a lower gate structure connected to a bottom surface of the first semiconductor layer by passing through the substrate.