Abstract: Disclosed is a method for manufacturing a self-aligned metal oxide thin film transistor. According to the present invention, a metal oxide semiconductor layer having a high carrier concentration is formed, and then a channel region which is self-aligned with a gate electrode is oxidized by a plasma having oxidbillity so that the channel region has a low carrier concentration and the source and drain regions have high carrier concentrations while the resulting transistor has a self-aligned structure. In addition, the threshold voltage of the transistor is controlled by the conditions under which the channel region of the transistor is subsequently oxidized by plasma having oxidbillity at a low temperature. Therefore, the controllability of the characteristics of the transistor is improved significantly, and the manufacturing process is simplified.