An array substrate, a display device and a manufacturing method. The array substrate includes a thin film transistor and a pixel electrode (9). The active layer (4) of the thin film transistor is formed by a first region (401) of the oxide semiconductor layer. The oxide semiconductor layer further includes a second region (402). The pixel electrode (9) and the second region (402) of the oxide semiconductor layer (9) are overlapped so as to form a storage capacitor. The second region (402) of the oxide semiconductor layer (9) constitutes a first electrode plate (402) of the storage capacitor; the pixel electrode (9) corresponding to the second region (402) of the oxide semiconductor layer (4) constitutes a second electrode plate (9) of the storage capacitor; and dielectric layers (7, 8) are disposed between the first electrode plate (402) and the second electrode plate (9).