This study investigates the shape transformation of 4H-SiC microtrenches that occurs during high-temperature hydrogen annealing, which is used to improve growth on such prepared substrates. The trenches have micron-sized widths and depths and were annealed in hydrogen ambient at temperatures of 1400-1600 degrees C for 30-3600 s. After hydrogen annealing, cross-sectional images of the samples were obtained by scanning electron microscopy (SEM). These SEM images reveal that the top and bottom trench corners become rounded during hydrogen annealing. The top trench corners become rounded by an etching reaction, whereas the bottom trench corners become rounded as a result of a regrowth phenomenon that involves the transportation of atoms. This study analyzes the mechanism of these transformations in terms of Mullins' continuum model. The results suggest that the evaporation-condensation process is dominant in the case of SiC annealing. (c) 2009 The Japan Society of Applied Physics