a 'solid-state' polyaniline-based microelectrochemical transistor is described. the transistor can be fabricated by the chemical modification of a microfabricated approximately 3 mm*3 mm chip consisting of an array of eight, individually addressable pt microelectrodes, each approximately 50 mu m long* approximately 2 mu m wide* approximately 0.1 mu m high and separated from each other by approximately 1.2 mu m. chemical modification of the chip consists of (1) placing a small spot of ag epoxy adjacent to the microelectrode array to serve as a quasi-reference electrode, (2) anodic polymerization of aniline to coat and interconnect six of the eight microelectrodes with redox-active polyaniline, and (3) overcoating the entire chip with a thin film of poly(vinyl alcohol)/h/sub 3/po/sub 4/, which serves as a solid-state electrolyte. the transistor function can be demonstrated by letting every other polyaniline-coated microelectrode serve as the source and the other three electrodes serve as the drain