A thin film transistor and a method for manufacturing the same, an array substrate and a display device that can prevent the semiconductor layer in a channel region from damage. The thin film transistor includes a gate electrode, a gate insulating layer, a semiconductor layer, an insulator layer, and source/drain electrodes, the insulator layer is provided on the semiconductor layer, covers channel regions of the source/drain electrodes, and is formed of a metal oxide insulator. In this thin film transistor, when water vapor from the air penetrates, the insulator layer formed of the metal oxide insulator will firstly reacts with the water vapor to prevent the metal oxide semiconductor in the channel region from damage.