An aqueous dispersion of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) was cast on screenprinted gold substrates. PEDOT(PSS) was ionically (physically) crosslinked by multivalent cations, including Mg 2+ , Ca 2+ , Fe 2+/3+ and Ru(NH 3 ) 6 2+/3+ to form a hydrogel in order to decrease the water solubility of the PEDOT(PSS). The resulting Au/PEDOT(PSS) electrodes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and energy-dispersive X-ray analysis (EDXA). Ionic crosslinking of PEDOT(PSS) with Fe 2+/3+ and Ru(NH 3 ) 6 2+/3+ was faster than with Mg 2+ and Ca 2+ ions and resulted in PEDOT(PSS) films that were less soluble in water. Among the multivalent cations tested, Ru(NH 3 ) 6 2+/3+ resulted in PEDOT(PSS) films with the most stable potential. Incorporation of Ru into PEDOT(PSS) was shown by EDXA. Based on CV and EIS, ionic crosslinking of PEDOT(PSS) with the electroactive Ru(NH 3 ) 6 2+/3+ was found to increase the bulk redox capacitance of the PEDOT(PSS) film, compared to ionic crosslinking with electroinactive Mg 2+ ions. Potentiometric measurements showed that PEDOT(PSS) ionically crosslinked with Ru(NH 3 ) 6 2+/3+ was less sensitive to CO 2 (pH) than the bare Au substrate. The Au/PEDOT(PSS) electrodes were found to work well as ion-to-electron transducer (solid contact) in all-solid-state K + -ion-selective electrodes (ISEs).