Insulated gate semiconductor device includes drift layer of first conductivity type; first base region of second conductivity type on the drift layer; carrier-supply region of the first conductivity type on the first base region and having higher impurity concentration than the drift layer; a first contact region of the second conductivity type on the first base region and having higher impurity concentration than the first base regions; cell-pillars each having polygonal-shape, arranged in a lattice-pattern, sidewalls of the cell-pillars are defined by trenches penetrating the carrier-supply region, the first contact region, and the first base region; and insulated-gate electrode-structures in the trenches. A first pillar selected from the cell-pillars includes the carrier-supply region, the first contact region and the first base region, and the first contact regions are in contact with a limited portion of an outer periphery of a first pillar at a top surface of the first pillar.