In an organic light emitting diode (OLED) display and a manufacturing method thereof, the OLED display includes a substrate main body; an insulation layer pattern formed on the substrate main body, and including a first thickness layer and a second thickness layer thinner than the first thickness layer; a metal catalyst that is scattered on the first thickness layer of the insulation layer pattern; and a polycrystalline semiconductor layer formed on the insulation layer pattern, and divided into a first crystal area corresponding to the first thickness layer and to a portion of the second thickness layer adjacent to the first thickness layer and a second crystal area corresponding to the remaining part of the second thickness layer. The first crystal area of the polycrystalline semiconductor layer is crystallized through the metal catalyst, and the second crystal area of the polycrystalline semiconductor layer is solid phase crystallized.