We report on the implementation of a robust and reproducible electrochemical CV (ECV) characterization for the (Al,In)GaN material system. A Schottky-like contact is formed by electrolyte, wetting the area of the semiconductor surface delimited by a sealing ring. In reverse bias with common CV technique the concentration of donors and acceptors can be evaluated. Using a newly developed etch procedure, which we call “cyclic oxidation” nitrides can be etched (photo-)electrochemically (PEC) to yield reproducibly etched surfaces with mirror-like surface morphology at high etch rates (∼3 µm/h). This new etch procedure is not restricted to n-type nitrides, but works also for p-type nitrides. In the first time cycle the nitride semiconductor is electrochemically oxidized: UV illumination and forward voltage is applied to oxidize n-GaN and p-GaN, respectively. During this time cycle the local pH-value of electrolyte at etch area decreases. The established thin oxide film – essential for smooth etching - is dissolved by jet-pumping with fresh electrolyte during the complementary time cycle. The influence of the process parameters on the etch rate is discussed. The application of this new etch procedure to characterize various MOVPE and HVPE grown samples by CV-Profiling is presented. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)