A monolithic potentiostat for chemical and biochemical sensors is presented. It allows measurements that use two- or three-clectrode-configurations in amperometric and voltammetric mode. The amplification part converts the electrode current with an input range from +/-0.1 InA up to +/-0.5/splmu/A. The microchip is fabricated in a 1/spl mu/m/5V Low Power Silicon-Gate CMOS process. The small chip size allows the assembly of the potentiostat together with monolithic microelectrodes on the same substrate. This way the distortion of the electrode signal is minimized, and the resulting rnicrosystem can be used as a low cost mass product for selective analysis, e.g. in very narrow passages.