A thin film transistor, an array substrate including the thin film transistor and a display device. The thin film transistor includes: a gate electrode (100), a gate insulating layer (200), an active layer (300) and a source/drain layer (400) that are successively stacked. The source/drain layer (400) comprises a source electrode (401) and a drain electrode (402) with a gap therebetween, and the active layer (300) forms a channel (301) in a region corresponding to the gap. The gate electrode (100) has a gate electrode protrusion (101) on at least one side of the channel (301) in its width direction; and the gate insulating layer (200) covers the gate electrode (100) and the gate electrode protrusion (101).