We report fabrication processes to realize freestanding GaN micromechanical structures on silicon-on-insulator (SOI) substrates. GaN layers were grown on (100) SOI substrates by metallorganic chemical vapor deposition. Prior to GaN growth, the surface of thin SOI overlayer was subjected to KOH treatment to expose {111} lattice planes. High-resolution X-ray diffraction, photoluminescence, and micro-Raman measurements were used to characterize these wurtzite GaN films. Using the combination of dry and wet etching techniques for surface micromachining, we have succeeded in releasing freestanding GaN structures on SOI platform. Such an approach is suitable for the fabrication of GaN-based microelectromechanical systems. (c) 2005 The Electrochemical Society.