The etching behavior and emerging facets of Si(110) convex corner anisotropically etched in KOH/KOH + isopropyl alcohol (IPA) solutions are investigated. A two-dimensional (2-D) zoning model, in which the undercut planes arising at a masked convex corner are presumed to be at the same zone of the sidewalls forming that convex corner, is employed in conjunction with the use of the Si(110) stereogram, Wulff net, and analytical geometry to determine the Miller indexes of the undercut planes. The theoretical results are verified by experimental measurement. With the two mask openings (one is the top-inverted of the other) being the same, the stereographically projected poles of the undercut planes of one masked corner etched in KOH plus IPA solution are mirror-symmetric in the 2-D Si(110) stereogram to those of the other masked corners. While the pure KOH aqueous solution produces the undercut planes of the two masked corners with poles being inversely symmetric, this discrepancy can be interpreted successfully by the proposed zoning-model theory. Although the atom-packing density of silicon of (110) orientation is less dense than that of (100) orientation, the zoning behavior of the undercut planes for Si(110) is the same as that of Si(100). (C) 2008 The Electrochemical Society.