An organic light emitting display device includes a substrate, a buffer layer, an active layer, a gate insulation layer, a protective insulating layer, a gate electrode, an insulating interlayer, source and drain electrodes, and a sub-pixel structure. The buffer layer is disposed on the substrate. The active layer is disposed on the buffer layer, and has a source region, a drain region, and a channel region. The gate insulation layer is disposed in the channel region on the active layer. The protective insulating layer is disposed on the buffer layer, the source and drain regions of the active layer, and the gate insulation layer. The gate electrode is disposed in the channel region on the protective insulating layer. The insulating interlayer is disposed on the gate electrode. The source and drain electrodes are disposed on the insulating interlayer.