We demonstrate a technique to reduce the extended defect densities in a-plane GaN deposited on r-plane sapphire. The SiO2 lateral epitaxial overgrowth mask consisted of < 1100 >(GaN) stripes. Both the mask and GaN were etched through the mask openings and the lateral growth was initiated from the etched c-plane GaN sidewalls, and the material was grown over the mask regions until a smooth coalesced film was achieved. Threading dislocation densities in the range of 10(6)-10(7) cm(-2) were realized throughout the film surface. The on-axis and off-axis full width at half maximum value and surface roughness were 0.082 degrees, 0.114 degrees, and 0.622 nm, respectively. (c) 2006 American Institute of Physics.