The subject of this thesis is the development and the characterization of threedimensional electrode arrays for the electrostimulation of neural cells. For the development of the electrode fabrication process special attention was paid to the compatibility with existing CMOS processes. This allows the fabrication of electrodes and electronic control circuitry on the same substrate in a close distance without the need of further assembly techniques. The fabrication process of the electrode arrays essentially consists of electrodeposition of gold to form the threedimensional electrode structures and a further electrodeposition of iridium in order to improve the electrode characteristics significantly. Cylic voltammetry and impedance measurements were performed to characterize and compare the fabricated iridium electrode arrays with other common electrode materials such as platinum, gold and titanium nitride. It was shown that the iridium electrodes have lower impedances over the considered frequency ranges and higher permissible clamp voltages for electrostimulation. Furthermore a method and a device for scanning potential microscopy was developed. Measurements of the local potential distribution of different electrode configurations and electrode shapes in saline solutions have been performed using this scanning potential microscope. In this way results obtained by finite element simulations have been verified experimentally. It was also shown that the presented method offers a better spatial resolution than previously reported methods.