A superjunction device in which corner portions of each annular-shaped second trench are composed of a plurality of alternately arranged first sides and second sides. The first sides are parallel to a plurality of parallel arranged first trenches in a current-flowing area, while the second sides are perpendicular to the first sides and the first trenches. Such design ensures that Miller indices of sidewalls and bottom face of any portion of each second trench belong to the same family of crystal planes. Moreover, with this design, the corner portions of the second trenches can be filled with a silicon epitaxial material at the same rate with the rest portions thereof, which ensures for the second trenches to be uniformly and completely filled without any defects in the corner portions and hence improve the performance of the superjunction device.