Epitaxial lateral overgrowth (ELO) GaN samples were successfully grown on masked sapphire (0 00 1) substrates using an in-situ carbonized photoresist (PR) mask by a metalorganic chemical vapor deposition (MOCVD) method. The PR masks for the ELO process were prepared using conventional lithography in the form of a stripe with an opening of 4 mu m and a period of 16 mu m. The stripe-patterned PR was annealed at 1000 degrees C in a H(2) atmosphere. The stripes were aligned parallel to the [11-20](Al2O3) direction. The ELO process of GaN was strongly dependent on the direction of the stripes. Overall, the PR masks on the sapphire substrate were carbonized during the heating step before the main growth, so that the carbonized PR mask acted as an ELO mask. The study results confirmed the promising potential of the ELO process using an in-situ carbonized PR mask as a single-step technique. (C) 2011 Elsevier B.V. All rights reserved.