A method of manufacturing transistor having a first and second thin film transistor by creating the second thin film transistor by forming a second gate of the second thin film transistor on a substrate, depositing an insulating layer and a semiconductor layer in order to cover the second gate. A photoresist layer is deposited above the semiconductor layer and exposed. The semiconductor layer and the insulating layer are etched, thereby forming a second active layer of the second thin film transistor and a first connection window disposed above the second gate. A second source and a second drain of the second thin film transistor is deposited above the insulating layer and the second active layer. The present method enables the manufacturing of an organic light emitting diode display. The method reduces the times of using a photomask, thereby saving the manufacture time, improving the productivity and economizing the manufacture cost.