An organic light emitting display and method of fabricating thereof, the display including a substrate including a first thin film transistor region and a second thin film transistor region; a buffer layer on the substrate; a first and a second semiconductor layer on the buffer layer; a gate insulating layer on the substrate; gate electrodes on the gate insulating layer and corresponding to the first semiconductor layer and the second semiconductor layer, respectively; source/drain electrodes insulated from the gate electrode and being connected to the first semiconductor layer and the second semiconductor layer, respectively; an insulating layer on the substrate; a first electrode connected to the source/drain electrode electrically connected to the first semiconductor layer; an organic layer on the first electrode; and a second electrode on the organic layer, wherein portions of the buffer layer corresponding to a source/drain region of the first semiconductor layer include a metal catalyst.