A method for manufacturing a semiconductor device, comprising: - preparing a first conductivity type semiconductor substrate having a principal surface and a back surface at an opposite side of the principal surface; - forming a first trench in the semiconductor substrate, the first trench extending in the semiconductor substrate from the principal surface in a perpendicular direction with respect to the principal surface; - forming a second conductivity type base region by filling up the first trench with a second conductivity type semiconductor; - forming a second trench within the base region and a third trench in the semiconductor substrate at a location remote from the base region, each of the second trench and the third trench extending from the principal surface in the perpendicular direction; - forming a first conductivity type source region by filling up the second trench with a first conductivity type semiconductor, and forming a first conductivity type drain region by filling up the third trench with the first conductivity type semiconductor, wherein the semiconductor substrate comprises a drift region (1 c) at an opposite side of the base region with respect to the source region; - forming a fourth trench penetrating the base region in a direction, which is parallel to the principal surface, from the source region, the fourth trench extending from the principal surface in the perpendicular direction; - forming a gate insulating film in the fourth trench; - forming a gate electrode on a surface of the gate insulating film; - forming a source electrode electrically connected to the source region and the base region; and - forming a drain electrode electrically connected to the drain region. - preparing a first conductivity type semiconductor substrate having a principal surface and a back surface at an opposite side of the principal surface; - forming a first trench in the semiconductor substrate, the first trench extending in the semiconductor substrate from the principal surface in a perpendicular direction with respect to the principal surface; - forming a second conductivity type base region by filling up the first trench with a second conductivity type semiconductor; - forming a second trench within the base region and a third trench in the semiconductor substrate at a location remote from the base region, each of the second trench and the third trench extending from the principal surface in the perpendicular direction; - forming a first conductivity type source region by filling up the second trench with a first conductivity type semiconductor, and forming a first conductivity type drain region by filling up the third trench with the first conductivity type semiconductor, wherein the semiconductor substrate comprises a drift region (1 c) at an opposite side of the base region with respect to the source region; - forming a fourth trench penetrating the base region in a direction, which is parallel to the principal surface, from the source region, the fourth trench extending from the principal surface in the perpendicular direction; - forming a gate insulating film in the fourth trench; - forming a gate electrode on a surface of the gate insulating film; - forming a source electrode electrically connected to the source region and the base region; and - forming a drain electrode electrically connected to the drain region.