A new technique for highly controllable trench corner rounding (TCR) at top and bottom of the trench using pull-back and hydrogen annealing has been developed and investigated. The pull-back process combined with hydrogen annealing can control the TCR radius at the top corners of the trench. The silicon migration generated by hydrogen annealing at the trench corners provides (111) and (311) crystal planes and gives a uniform gate-oxide thickness, resulting in highly reliable trench gate DMOSFETs with high breakdown voltages and low leakage currents. The gate breakdown voltage of a trench DMOSFET fabricated by using hydrogen annealing was 27V, which was 22% higher than that of no hydrogen-annealed devices. The on-resistance of the trench gate DMOSFET fabricated by using the trench cell of 45,000 is about 5 5 mOmega at a gate voltage of 10 V under a drain current of 5 A. (C) 2003 Elsevier Science B.V. All rights reserved.