We propose a new structure of power MOSFET, i.e. Super Trench power MOSFET (STM). Instead of a conventional ndrift layer, STM hasvertical P and N layers formed within mesa regions between adjacent trenches filled with insulator. The P and N stripe structure relaxes the electric field[l-3) in off-state and makes possible a lower specific on-resistance (Ron, sp) than that of the conventional MOSFET. We fabricated a 250V STM for the first time with only one additional mask over the conventional DMOS process, and the measured data show high breakdown voltage with highly doped n drift layer. The device simulation results show it should be possible to lower the Ron,sp to 5mQcm' for a breakdown voltage of 300 V. (?Source I O D r a in

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