This article describes the influence of electrode geometry on the response of solid-contact ion-selective electrodes (SC-ISE) with a conducting polymer (CP) as solid contact, when using a recently reported signal readout method based on constant potential coulometry. Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) was electropolymerized on glassy carbon disk electrodes with areas ranging from 0.031 cm2 to 0.79 cm2. The polymerization charge was kept constant (1 mC) for all electrodes, meaning that the redox capacitance of PEDOT was constant for all electrodes while the PEDOT thickness decreased with increasing electrode area. The thickness of the K+-selective membrane covering the CP was kept constant, so that the total resistance of the K+-selective membrane decreased with increasing electrode area. When utilizing the coulometric signal readout method, the response time of the SC-ISEs was significantly shortened by increasing the electrode area.