The large interfacial area of the porous silicon is used as ion sensitive membrane support. The porous layer is oxidized by Rapid Thermal Oxidation (RTO) technique and a calix(4)arene layer was evaporated under vacuum. The structure is then used as the working electrode of an electrochemical cell and sensor properties were investigated by capacitance measurements. We observed an over-Nernstian response of the coated porous silicon to the Na + ion.