Silicon carbide (SiC) single crystals, a promising material for high power and high temperature semiconductor devices, suffer from crystallographic hollow defects, so-called "micropipes." Their formation mechanism is not satisfactorily clarified yet. In this paper, we propose a micropipe formation model via surface step interaction, where the strong repulsive interaction between surface steps on the SiC(0001) surface is a major driving force for coalescing unit cell size screw dislocations.