This paper reports on the electrochemical and photo(electro) chemical fabrication of single-crystalline InP membranes with homogeneous surfaces allowing for adjustable pore shapes from roundish to square-like and various surface morphologies from extremely flat to cone-like pore wall tips. The InP membrane thickness is tunable from several tens of mu m to almost 500 mu m. FFT impedance data measured in-situ during pore etching can be easily fitted by an RC-component in series with a resistor and allow for precise in-situ prediction of the final membrane surface morphology and easy process parameter adjustment for the production of membranes with arbitrary membrane thicknesses. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.041211jes] All rights reserved.