The etch pits of three different types of dislocations in low-doped homoepitaxial layers have been investigated by KOH etching, optical microscopy, synchrotron white beam X-ray topography (SWBXT), scanning electron microscopy (SEM), and atomic force microscopy (AFM). A simple method by KOH etching and polishing for monitoring elementary screw dislocations in SiC epilayers is proposed. The etch pits of threading screw dislocations were larger and deeper than those of threading edge and basal plane dislocations. The size and depth differences became more pronounced with increase of etching time. The small etch pits of threading edge and basal plane dislocations could be removed selectively by polishing, leaving only the pits of screw dislocations. It is proposed that this technique can be applied to assess the screw dislocation density in a large area and to trace the screw dislocations.