We describe an integrated CMOS electrochemical sensor with on-chip electrodes and packaging. The CMOS chip was fabricated in a standard 0.5 μm CMOS process, and it contains potentiostat circuits with integrated array of three electrode cells. In the potentiostat circuit, we designed high performance folded cascode class-AB operational amplifiers with rail to rail input and output suitable for low power consumption and strong drive capability. The 1.5 mm × 3 mm potentiostat array chip operates from a 5 V supply at 45 μA. A gold electrode array was made on the surface of the CMOS chip using a contact photolithographic process. For compatibility with liquid test environments a packaging approach was developed. The electrochemical sensor with on-chip electrodes was characterized by using cyclic voltammetry (CV) with potassium ferricyanide.