In radial expansion growths of 6H-SiC crystals, crevasse-like microcrack defects are found to be formed in the expansion region of the crystal when the lateral growth component becomes predominant. Detailed microstructural observation has revealed that the crevasse-like defect consists of the minor facet planes, presumably {1-102} and {1-104} of 6H-SiC. We deduce from the results obtained that, although further investigation is still needed for understanding of the formation mechanism, subgrain boundaries existing in the seed crystals could trigger the subsequent formation of the minor facet planes, giving rise to the appearance of the crevasse-like defect observed.