An organic light emitting display that prevents a material used to form a source electrode and a drain electrode from being diffused into an active layer and reduces contact resistance between the source and drain electrodes and a first electrode includes: a substrate; an active layer arranged on the substrate and including silicon; a gate electrode arranged on the substrate and insulated from the active layer; a source electrode and a drain electrode each of a single layer structure, insulated from the gate electrode, and electrically connected to the active layer; a first electrode electrically connected to either the source electrode or the drain electrode; an organic light emitting layer arranged on the first electrode; and a second electrode arranged on the organic light emitting layer, each source electrode and drain electrode includes an aluminum alloy containing nickel and silicon.