We report a new type of solid-state electrode (type I) of a simple design with polyvinyl chloride membranes based on Mn(III) tetraphenylporphyrin and with graphite as the electronically conducting substrate. Enlargement of the membrane/graphite contact area by soaking graphite in the plasticizer with subsequent conditioning of the electrode at 30 °C allowed us to shorten the time required to achieve steady potential values of the sensors to just 3 days. These electrodes do not require a specially added RedOx system in the transducer layer. Stabilization of the EMF response of type I electrodes is compared to type II electrodes which contain a Cu⁰/Cu²⁺ RedOx couple in the transducer layer. Type I sensors are suitable for measuring the salicylate ion concentration in the clinically important concentration range down to 2.5 × 10⁻⁴ M with a sensitivity to salicylate ion of −59.0 mV decade⁻¹ in solutions with a high constant background of chloride ions of 0.12 M at pH = 5.3, making this a promising technique for an effective design of solid-contact ion-selective electrodes with polymeric sensing membranes. [Figure not available: see fulltext.].