A TFT, a method for fabricating the same, a display substrate, and a display device are disclosed. The TFT comprises a substrate, a gate, a gate insulating layer, semiconductor layer, a source, and a drain. The gate comprises a rough surface on a side facing the semiconductor layer. Since the surface of gate is uneven, the light which has been reflected on the surface of gate will no longer be reflected, or will be directly scattered to other directions. The incident light from the backlight source cannot impinge onto the semiconductor layer by continuous reflection. This reduces the possibility that the semiconductor layer is irradiated by light, and improves stability of TFT.