A wide range of applications in neurotechnological research rely on planar microelectrode arrays (MEA) but the disadvantage of these systems is the low density of electrodes caused by the problem of wiring a great number of electrodes. In turn this results in a low number of good cell to electrode contacts. To overcome this drawback, a great number of laterally isolated sub-um electrodes is placed on a photoconductor layer (amorphous silicon a-Si:H). By use of a laser beam, only those sub-um electrodes lying under the cell can be selected to form an electrical contact to one of the underlying indium tin oxide (ITO) leads providing a high seal resistance at the cell / electrodes interface. A biocompatible and biostable composite layer of electrodes (100–500 nm) and insulator is formed using nanostencil-technology. Dark to bright ratio D of the photoconductor is determined to 10^5 – 10^6 . The impedance of Au and TiN sub-um electrodes in physiological solution is measured. Spatial resolution of the system is limited by light-scattering inside the supporting glass substrate; the effective diameter of the conductive region illuminated by the laser spot with intrinsic diameter 1.6 um is 6–7 ~um.