It has been reported recently that the sapphire Substrate can be etched inside a metalorganic chemical vapor deposition reactor through GaN decomposition-induced reaction, and that device-quality GaN films can be grown on thus etched substrates with residual gallium droplets acting as nucleation sites [Hao et al., Appl. Phys. Lett 84 (2004) 4041]. In the present study, a maskless lateral epitaxial over growth (LEO) method is proposed to produce GaN films with reduced dislocation density through the use of in situ etched sapphire substrates. The microstructure of such GaN films was investigated by transmission electron microscopy and scanning electron microscopy, and the effect of lateral over growth has been confirmed. Dislocations in such GaN films were further analyzed through etch-pits density experiment and it has been found that this maskless LEO method is very effective to reduce pure edge dislocation density in the GaN films. (c) 2005 Elsevier B.V. All rights reserved.