This paper describes a study of the electrical properties of supported lipid bilayer membranes on semiconductor and gold surfaces. The study is aimed to foster the understanding of supported membrane systems and to allow the rational design of biosensor assays for ion channel analysis. Impedance spectroscopy was applied for the electrical characterization of the supported membrane systems. A novel equivalent circuit model is introduced for the data evaluation, which accounts for the deviation of the impedance response of supported membranes from that of an ideal RC element. As a result of the improved accordance of model and data, the resistance and the capacity of supported membranes can be determined more accurately and independently from each other. Experimental results describe the phenomenology of the electrical properties of supported bilayers regarding variations in preparation, composition, and environmental conditions. We discuss the findings in terms of membrane−substrate interactions and models of membrane permeability. The important role of the electrostatics between the lipid bilayer and the solid substrate for the formation of an electrically dense supported membrane is identified. Bilayer permeability models explain the correlation between the structure of the lipid bilayer and its insulating properties. These models are also in accordance with the observed dependence of the electrical resistance of the lipid bilayer on the temperature and the ion concentration of the electrolyte.