A method of manufacturing a display device including forming a polysilicon layer on a substrate, patterning the polysilicon layer to form a polysilicon pattern including a first region and a second region each having a first thickness, and a third region having a second thickness less than the first thickness, forming a gate insulation layer on the polysilicon pattern, forming a gate electrode on the gate insulation layer, partially implanting ions into the polysilicon pattern to form an active layer, forming an insulation interlayer on the gate electrode, forming source and drain contact holes each passing through the insulation interlayer and the gate insulation layer and respectively overlapping the first region and the second region, forming source and drain electrodes respectively filling the source and drain contact holes, and forming a light emitting element electrically connected to the source electrode or the drain electrode.