Due to their fragility, classical ion-selective electrodes (ISEs) can be replaced by a new generation of chemical sensors. In this work, all-solid-state potassium selective electrodes, based on a plasticized poly(vinyl chloride) (PVC) membrane and a Prussian blue film as the solid internal contact, were prepared and characterized. First of all, potentiometric measurements revealed a non-Nernstian response of the electrode. Then, ac electrogravimetric measurements were carried out in KCl solutions under various polarization potentials. It was clearly found that potassium ions enter the PVC membrane regardless of the potential applied. Moreover, small quantities of solvent also enter the membrane at certain studied potentials. Electroacoustic measurements have been also carried out in order to check the validity of Sauerbrey's law for the quartz crystal microbalance by estimating the electrical characteristics of the quartz resonator under our experimental conditions.