A technique relates to a semiconductor device. First metal contacts are formed on top of a substrate. The first metal contacts are arranged in a first direction, and the first metal contacts are arranged such that areas of the substrate remain exposed. Insulator pads are positioned at predefined locations on top of the first metal contacts, such that the insulator pads are spaced from one another. Second metal contacts are formed on top of the insulator pads, such that the second metal contacts are arranged in a second direction different from the first direction. The first and second metal contacts sandwich the insulator pads at the predefined locations. Surface-sensitive conductive channels are formed to contact the first metal contacts and the second metal contacts. Four-terminal devices are defined by the surface-sensitive conductive channels contacting a pair of the first metal contacts and contacting a pair of the metal contacts.