Copper-rich, chemically and mechanically stable Cu-As-Se ultrathin films (15−30 nm) have been prepared by r.f. co-sputtering of the host and metallic copper and characterized by XPS, AES and RBS. Cu 2+ -selective chemical sensors based on the sputtered films have been fabricated, and their sensor characteristics investigated in a static electrochemical cell and in a flow-through microcell. The developed sensors exhibit near-Nernstian response over six orders of magnitude, a low detection limit below 10 −7 M (6 ppb), high reproducibility of the sensor potentials and high selectivity in the presence of alkali, alkaline earth and heavy-metal ions. The sensors remain highly sensitive and selective during continous measurements over at least six weeks.