An organic light emitting device includes a switching transistor and a driving transistor. A semiconductor layer is commonly used by the switching and driving transistors. The portion of semiconductor layer corresponding to the driving transistor is curved. A gate insulating layer is located between a channel region and gate electrode of the switching transistor, and between the channel region and the gate electrode of the driving transistor. The gate insulating layer has substantially a same plane shape as the switching gate electrode and the driving gate electrode. An edge of the gate insulating layer and an edge of the switching and driving gate electrodes at least partially overlap.