An organic thin film transistor (OTFT) having a patterned organic semiconductor layer on top of an electrode wiring layer. In order to avoid damage to the underlying electrode wiring layer, the organic semiconductor layer is patterned so that none of the organic semiconductor layer is removed off the electrode wiring layer. The patterned organic semiconductor layer completely covers all of the underlying electrode wiring layer. The OTFT includes a gate electrode, source and drain electrodes insulated from the gate electrode and an organic semiconductor layer which is insulated from the gate electrode and is in contact with the source and drain electrodes, wherein the organic semiconductor layer completely covers the source and drain electrodes. In addition, an organic light emitting display device includes more than one OTFT as well as an organic light-emitting element electrically connected to the electrical conductor.