We have investigated the effect of high temperature hydrogen annealing on the sidewall morphology of micron-sized trenches formed on a Si(0 0 1) substrate by atomic force microscopy. We show that high temperature hydrogen annealing is effective for the flattening of as-etched rough surfaces and yields surfaces having atomic steps and terraces when the annealing temperature exceeds 1000 degreesC. We also found that, during hydrogen annealing, large-scale structural changes accompanied trench corner rounding and occurred through the movement of steps on the sidewall surfaces. (C) 2004 Elsevier B.V. All rights reserved.