An organic semiconductor light emitting device wherein efficiency of injecting a carrier from an organic semiconductor active layer to an organic semiconductor light emitting part is improved. The organic semiconductor light emitting device includes the organic semiconductor active layer having a source area and a drain area set at an interval of a channel length, a source electrode joined to the source area, the organic semiconductor light emitting part joined to the drain area, a drain electrode joined to the organic semiconductor light emitting part, and a gate electrode arranged to face the organic semiconductor active layer with an insulating film interposed. The organic semiconductor light emitting part includes an organic semiconductor light emitting layer which receives electrons and holes from the drain electrode and holes from the drain electrode and the organic semiconductor active layer and generates light by recombination of the electrons and the holes.