An array substrate and a display device are provided. A gate insulating layer and a gate electrode are formed on a semiconductor layer in sequence, the gate insulating layer and the gate electrode are located in a middle position of the semiconductor layer and have a uniform shape and size. In a region on the semiconductor layer that is not covered by the gate insulating layer, there is further provided a metal diffusion layer. A barrier layer includes a portion covering the gate insulating layer and the gate electrode and a portion located around the semiconductor layer. A passivation layer covers the semiconductor layer, the gate insulating layer, the gate electrode and the barrier layer. Source and drain electrodes are connected to the metal diffusion layer respectively, and a pixel electrode contacts with the drain electrode.