The breakdown capability of the trench superjunction (SJ) VDMOS with strip gate and rounded corner layout pattern is experimentally investigated. The investigation shows that the local charge imbalance of device's corner is the reason for breakdown voltage degradation. In order to improve the breakdown capability and reliability of the device, an analytical model which is verified by the simulation using Sentaurus TCAD and experiment results is proposed to optimize the doping of p-pillar with respect to different cell pitches and corner radiuses. Finally, two robust 600 V trench SJ-VDMOS structures with different curvatures of the corner are proposed and fabricated. (C) 2011 Elsevier Ltd. All rights reserved.