An organic semiconductor device includes a substrate, a gate electrode formed directly on the substrate , gate insulating film formed directly on the gate electrode, a source electrode and a drain electrode formed directly on the gate insulating film, an organic semiconductor layer formed directly on the source electrode and the drain electrode, and a voltage control layer disposed directly between the gate insulating film and the organic semiconductor layer and directly contacting the source electrode and the drain electrode, wherein the voltage control layer gives an ambipolar characteristic to the organic semiconductor layer.