n-Type GaP was anodized in bromide-ion-containing solutions. In these solutions pores can be grown into the GaP substrate with morphologies that depend strongly on the electrochemical parameters. Under specific potentiostatic conditions highly defined rectangular pores can grow perpendicular to the (100) surface forming several micrometer thick well-defined porous layers on GaP. The etched channels show an etch stop at the (110) planes, a self-organized arrangement with a rectangular cross section of (233 +/- 8) nm x (327 +/- 10) nm and a typical spacing of 400 nm. (c) 2005 The Electrochemical Society.