Gallium nitride (GaN) material system has been developed for a broad range of applications involving light emitting diodes (LEDs), laser diodes, solar cells, and high power electronic devices due to its unique mechanical, electronic, and optical properties. Many approaches have been employed to enhance the performance of GaN-based optoelectronic devices. Especially, surface texturing techniques can be a candidate to overcome the total reflection at the interface between air and GaN surface. Poor light extraction is attributed to the significant difference in the refractive index between air (n=1) and GaN (n=2.5).To develop novel etching techniques, GaN samples with various polarities and two types of etchants were used. First, both Ga-polar and N-polar GaN thin films were used to study the effects of chemical etching. The Ga-polar GaN was chemically stable for KOH solutions while KOH could etch the N-face in contrary. Hexagonal pyramids were observed on N-polar GaN surface after the etching process. On the other hand, the N-polar surface of GaN showed dodecagonal pyramids when using H3PO4 solutions. The hexagonal and dodecagonal pyramids coexist on the etched surfaces when using a low concentration of H3PO4 solution. A study of bulk GaN allows a direct comparison of the ± c-planes but the standard epitaxial growth exhibits a moderate level of dislocations and high level of strain. So, stress-free low-defect GaN micro-wires are useful instruments to investigate the etch behaviors of GaN along the growth directions including the polar c-planes and the nonpolar m-planes. Nonpolar and semipolar GaN offer a route to eliminate or to minimize the polarization-induced problems in the polar GaN structures. Wet chemical etching using hot KOH and H3PO4 solutions was performed on semipolar (11-22) and nonpolar (11-20) GaN films grown on sapphire substrates. An alternating KOH/H3PO4/KOH etch process was developed to control the orientation of the facets on the thin-film surfaces. After the KOH etch process, c-plane and m-plane facets were reveled on the surfaces of both semipolar and nonpolar GaN. The next etch step in H3PO4 solution additionally exposed a (-1-12-2) plane, which is chemically stable in H3PO4 solution. After the fundamental study of chemical etching, these techniques were applied to actual GaN-based LEDs. Nonpolar a-plane GaN LEDs and freestanding GaN LEDs were used. Photoelectrochemical (PEC) wet etching produced unique features of etching morphology on the mesa sidewall faces and the n-type a-plane GaN surface. The freestanding LED structures were obtained by removing the patterned sapphire substrate using laser lift-off technique. The morphology of N-face GaN surface, which had been located between the sapphire and the GaN film, was changed by the chemical etching process in KOH and H3PO4 solutions. Flexible GaN-based LEDs on poly-ethylene terephthalate substrate are demonstrated. The roughened surfaces resulting from the chemical etch process enhanced extraction efficiency through multiple scattering events of photons and randomized the directions of the photons.