A method of manufacturing a transistor may include: forming a first well over a silicon substrate; forming a first mask pattern over the silicon substrate and using the formed first mask pattern to form a second well; removing the first mask pattern; forming a second mask pattern over the silicon substrate and using the formed second mask pattern to form a first drift region; removing the second mask pattern; forming a third mask pattern and using the formed third mask pattern to form a second drift region; removing the third mask pattern; forming a field oxide film over the silicon substrate; and introducing first conductive impurity ions into an upper surface of the silicon substrate by channel ion implantation.