4H-SiC epilayers are grown by chemical vapor deposition (CVD) under a various C/Si ratio of source gases. At a relatively low C/Si ratio, micropipes are dissociated into several closed-core screw dislocations in a high probability. Correspondingly, line-shaped surface depressions are generated at a relatively low C/Si ratio. Thus, based on the morphological observation on the epilayers grown under a various C/Si ratio, conditions and mechanisms for micropipe dissociation have been discussed.