Embodiments of the present invention provide a method for manufacturing a transistor, a transistor, an array substrate and a display device. The method comprises: forming a first source/drain metal layer on a substrate; forming an insulating layer above the first source/drain metal layer; forming a gate metal layer on the insulating layer; forming a gate insulating layer on the gate metal layer; forming a semiconductor layer above the gate insulating layer; forming an etching blocking layer on the semiconductor layer; forming a second source/drain metal layer above the etching blocking layer; forming an insulating layer above the second source/drain metal layer.