We have studied the effect of isoelectronic In-doping on the structural properties of GaN grown by pendeo-epitaxy. From an analysis of cross-sectional transmission electron microscopy (TEM) images, the threading dislocation originating from the (0001) facet of GaN seed layer, thereafter propagating onto the top surface of regrown GaN layer, were reduced due to isoelectronic In-doping, which could enhance vacancy trapping. In addition. threading dislocations in the coalescence region were not observable. These results indicate that these dislocations are bent or terminated in the boundary of coalesced region. Also, the crystalline quality was improved from the results of high resolution X-ray diffraction and TEM measurements.