In this work, a defect-selective etched nanoporous GaN was formed using electrochemical etching in oxalic acid and employed as a template for the overgrowth of high quality GaN epilayers by metal/organic chemical vapor deposition. To illustrate the influence of the nanoporous GaN on the subsequent overgrown GaN epilayer, high resolution X-ray diffraction (XRD) and transmission electron microscopy (TEM) were measured. The linewidth values of the XRD rocking curve for an overgrown GaN epilayer decreased both for the (002) symmetry plane and (102) asymmetry plane. The TEM observations indicated that the GaN epilayers overgrown on the nanoporous GaN templates had fewer threading dislocations (TDs) due to dislocation bending and had annihilated in the form of dislocation loops. The results indicate that the use of nanoporous GaN as a template is an effective way to reduce the density of TDs in GaN epilayers. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3526675] All rights reserved.