A vertical power transistor device comprising: a semiconductor layer (105, 305, 405) of a first conductivity type; a plurality of cylindrically-shaped dielectric regions (130, 230, 330, 430) disposed in the semiconductor layer, the cylindrically-shaped dielectric regions extending in a vertical direction from a top surface of the semiconductor layer downward, adjacent ones of the cylindrically-shaped dielectric regions being laterally separated along a common diametrical axis by a narrow region of the semiconductor layer having a first width, each cylindrically-shaped dielectric region (130, 230, 330, 430) having a cylindrically-shaped, conductive field plate member (150, 250, 350, 450) centrally disposed therein and laterally separating the cylindrically-shaped conductive field plate member (150, 250, 350, 450) from the narrow region; a source region (120, 220, 320, 420) of the first conductivity type disposed at the top surface of the narrow region of the semiconductor layer; a cell of the vertical power transistor device comprising a triad of adjacent cylindrically-shaped dielectric regions (130, 230, 330, 430) in a triangular arrangement; and a drain region (170, 370, 470) of the first conductivity type disposed beneath the semiconductor layer, characterized in that each cylindrically-shaped, conductive field plate member (150, 250, 350, 450) extends in the vertical direction from the top surface of the semiconductor layer downward to near a bottom of the cylindrically-shaped dielectric region (130, 230, 330, 430), and a dielectric-filled trench (210, 310) is formed between the triad of the adjacent cylindrically-shaped dielectric regions (130, 230, 330, 430). a semiconductor layer (105, 305, 405) of a first conductivity type; a plurality of cylindrically-shaped dielectric regions (130, 230, 330, 430) disposed in the semiconductor layer, the cylindrically-shaped dielectric regions extending in a vertical direction from a top surface of the semiconductor layer downward, adjacent ones of the cylindrically-shaped dielectric regions being laterally separated along a common diametrical axis by a narrow region of the semiconductor layer having a first width, each cylindrically-shaped dielectric region (130, 230, 330, 430) having a cylindrically-shaped, conductive field plate member (150, 250, 350, 450) centrally disposed therein and laterally separating the cylindrically-shaped conductive field plate member (150, 250, 350, 450) from the narrow region; a source region (120, 220, 320, 420) of the first conductivity type disposed at the top surface of the narrow region of the semiconductor layer; a cell of the vertical power transistor device comprising a triad of adjacent cylindrically-shaped dielectric regions (130, 230, 330, 430) in a triangular arrangement; and a drain region (170, 370, 470) of the first conductivity type disposed beneath the semiconductor layer, characterized in that each cylindrically-shaped, conductive field plate member (150, 250, 350, 450) extends in the vertical direction from the top surface of the semiconductor layer downward to near a bottom of the cylindrically-shaped dielectric region (130, 230, 330, 430), and a dielectric-filled trench (210, 310) is formed between the triad of the adjacent cylindrically-shaped dielectric regions (130, 230, 330, 430).