We have fabricated and characterized sandwich-type devices based on an oriented polythiophene derivative. Depending on the voltage sweep direction, the devices showed the presence of two conducting states. Switching between the two states and an associated memory have earlier been studied by current-voltage characteristics. In this article, we have studied impedance spectroscopy of the material to model the device. We have studied conductance switching by measuring capacitance of the device, and have probed the high- and low-conducting states of the device. It has been shown that voltage variation of dielectric constant of the material depends on the voltage sweep direction. We have also demonstrated that capacitance of the device can probe the two states for data-storage applications. (C) 2003 Elsevier B.V. All rights reserved.