Highly resistive planar supported lipid membranes were deposited onto highly doped p-type silicon-silicon dioxide electrodes. Physical parameters of the substrates (e.g. dopant, doping ratio and oxide layer thickness) were optimized by a combined study using ellipsometry and ac impedance spectroscopy. Lipid bilayer was deposited by fusion of small unilamellar vesicles, and the self-assembling of the homogeneous bilayer could be monitored as a function of time. Impedance spectroscopy over a wide frequency range (from 20 kHz to 10 mHz) enables separating membrane resistance and capacitance from the background signals. Membrane resistance amounted to 1.0 M Omega cm(2), and the capacitance was around 0.7 muF cm (-2). The resistance obtained here is comparable to that of the freestanding black lipid membrane. Although the area of the supported membrane (0.5 cm(2)) is much larger than that of the black lipid membrane ( similar to 0.002 cm(2)), the electrical properties were stable for more than a week. Gramicidin D was inserted into the membrane from trifluoroethanol solution, and activity of the channels was checked in terms of membrane conductance and ion selectivity. Functional incorporation of ion channels into the supported membrane demonstrated here suggested that the gramicidin monomers could diffuse over the membranes to form transmembrane pores.