The invention discloses a transistor and a method for forming the transistor. The method for forming the transistor comprises the steps that a semiconductor substrate is provided; a first pseudo grid structure is formed on the surface of a first area of the semiconductor substrate, and a second pseudo grid structure is formed on the surface of a second area of the semiconductor substrate; a battier layer, a first insulating layer and a second insulating layer are formed on the surface of the side wall of the first pseudo grid structure and the surface of the side wall of the second pseudo grid structure, wherein the first insulating layer is located on the surface of the barrier layer and contains oxygen, and the second insulating layer is located on the surface of the first insulating layer; the first pseudo grid structure and the second pseudo grid structure are removed, and a first groove and a second groove are formed; the portion, located on the surface of the side wall of the second groove, of the barrier layer is removed; a first grid structure is formed on the surface of the portion, located on the inner wall of the first groove, of the barrier layer; a second grid structure is formed on the surface of the portion, located on the inner wall of the second groove, of the first insulating layer. According to the method for forming the transistor, transistors with different voltage thresholds are formed in the first area and the second area of the semiconductor substrate, the technical processes are simple, and the performance of the transistors is improved.