A model is presented for the formation mechanism of dislocation half-loop arrays formed during the homoepitaxial growth of 4H-SiC. The reorientation during glide of originally screw oriented threading segments of basal plane dislocation (BPD) renders them susceptible to conversion into sessile threading edge dislocations (TEDs), which subsequently pin the motion of the BPD. Continued glide during further growth enables parts of the mobile BPD to escape through the surface leaving arrays of half loops comprising two TEDs and a short BPD segment with significant edge component. The faulting behavior of the arrays under UV excitation is consistent with this model.