The grooved c-plane sapphire substrates were first systematically investigated by wet chemical etching, with H2SO4 and a 3H(2)SO(4):1H(3)PO(4) mixture as the etchants. The structural and morphological characteristics of the grooved sapphire with mask stripes along the < 11 (2) over bar0 > and < 1 (1) over bar 00 > directions, respectively, were studied under different etching time and temperatures by scanning electron microscopy (SEM). Two kinds of groove shapes are obtained. One is a V-groove whose two sidewalls are both formed by a single facet. The other is a U-groove whose one sidewall consists of two or three facets, and the other sidewall is composed of a single facet. SEM cross-sectional images show symmetrical sidewall facets with stripes along the sapphire (1 (1) over bar 00) direction and asymmetrical sidewall facets with stripes along the sapphire < 11 (2) over bar0 > direction. The etching depth is linear with the etching time. The activation energies of etching reaction are evaluated in the temperature range 340-400 degrees C. It is confirmed that sapphire with stripes along the < 11 (2) over bar0 > direction is suitable for lateral epitaxial overgrowth of low-threading-dislocation GaN films. (c) 2006 The Electrochemical Society.