Sloped sidewalls in 4H-SiC mesa structures on the (000-1) C face were formed by a Cl2-O2 thermal etching method. The etching rate of 4H-SiC (000-1) C face was 10 times faster than that of (0001) Si face, and the etching rate at 910oC was about 18μm/h. The etched surface was rather smooth, and the sidewall of the mesa was inclined to the off-axis substrate. Taking into account the off angle of about 8o toward [11-20] off direction, the angles of the sidewalls were 52-56o for the <1-100> and 55-57o for the <11-20> directions from the crystallographically accurate (000-1) C face. Epitaxial pn junction diodes with the sloped sidewalls structure were fabricated, which had good electrical properties.