A two-step chemical wet etching processes were used to investigated the formation and the plane indexes of exposed etched facets of wet etching patterned sapphire substrate (PSS). It was found when SiO2 mask still remained on the top c-plane, the structure of PSS comprised of a hexagonal pyramid covered with six facets {3 (4) over bar 17} with a flat top c-plane. When SiO2 mask were etched away, beside six facets on the bottom, there were 3 extra facets {1 (1) over bar 05} exposed on the top. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.095206jes] All rights reserved.