A
transistor and a forming method thereof are disclosed. The forming method of the
transistor comprises the following steps: providing a substrate with a pseudo gate film on the surface;
etching part of the pseudo gate film in the thickness direction; after
etching part of the pseudo gate film in the thickness direction, forming a second initial pseudo gate layer and a plurality of first initial pseudo gate
layers on the surface of the second initial pseudo gate layer, wherein a first opening is formed between every two adjacent second initial pseudo gate
layers; oxidizing the sidewalls of the first initial pseudo gate
layers and the second initial pseudo gate layer on the bottoms of the first openings, forming a first
oxide layer on the sidewall surfaces of the first initial pseudo gate layers, and making the second initial pseudo gate layer on the bottoms of the first openings form a second
oxide layer and the remaining second initial pseudo gate layer and first initial pseudo gate layers form pseudo gates, wherein the bottom size of the pseudo gates is greater than the top size; forming a
dielectric layer on the surface of substrate, wherein the
dielectric layer exposes the top surfaces of the pseudo gates; removing the pseudo gates, and forming second openings in the
dielectric layer; and forming gate structures in the second openings. The performance of the formed
transistor is improved.