A manufacturing method of a semiconductor device includes the steps of: forming an insulating pillar on the main surface of a silicon substrate; forming a protective film on the side surface of the insulating pillar; forming a silicon pillar on the main surface of the silicon substrate; forming a gate insulating film on the side surface of the silicon pillar; and forming first and second gate electrodes so as to contact each other and so as to cover the side surfaces of the silicon pillar and insulating pillar, respectively. According to the present manufacturing method, the protective film is formed on the side surface of the insulating pillar as a dummy pillar, thus preventing the dummy pillar from being eroded when the silicon pillar for channel is processed into a transistor. Therefore, it is possible to reduce a probability of occurrence of gate electrode disconnection.