As neutral carriers for sodium ion-sensitive field-effect transistors (ISFETs), unsymmetrical calix[4]arene ionophores have been designed which possess three ester linkages and an amide linkage as the cation-binding sites. One of the calix[4]arene derivatives are highly soluble In silicone rubber, which is very adhesive to inorganic FET gates, thus affording stable sensing membranes for the ISFET. The resulting sodium ISFETs based on the calixarene ionophore/silicone rubber composite showed high sodium ion selectivity and high sensor durability.