Thermal etching of hexagonal (4H-, 6H-, 8H- and 10H-), rhombohedral (15R- and 21R-), and cubic (3C-) SiC Si-faces was performed between 900 and 1000oC in a mixed gas of chlorine (Cl2) and oxygen (O2). In the case of well oriented Si-faces, the 3C-SiC (111) substrate was etched fastest in polytypes. The etching rate in the dislocation-free area depended on the hexagonality. Etch pits with definite shapes appeared, which depend on the type of dislocation and crystal structures. On the basis of these results, etching properties are discussed.