In situ hydrogen etching is widely used to remove the damaged layer and improve the surface finish of SiC substrates for epitaxy. In this work, the change of dislocation density in 6H-SiC substrates subjected to hydrogen etching and treatment in argon atmosphere at 1650degreesC was studied. The hydrogen etching conditions effective in producing an atomically flat, damage-free surface were found to increase the dislocation density of the sample up to 20%. However, the dislocation density decreased up to 25% when treated in argon atmosphere instead of hydrogen. In both cases, clear movement of micropipes, planars and dislocations was observed. The preferred directions of movement were <11 (2) over bar0> towards the nearest edge of the sample. The increase of the dislocation density during hydrogen etching is explained in terms of the release of stress associated with micropipes, screw dislocations, and sub-surface damage layer removal.