The energy storage of activated carbon modified with a semiconducting oxide TiO2 is studied. The composite was prepared by mixing nanosize TiO2 and activated carbon through a means of ultrasonic vibration in ethanol solution for 30 min. It was found that with modification of TiO2, the specific capacitance of activated carbon measured at 0.65 mA/cm(2) was increased from 47.2 to 63.1 F g(-1). This method is unique in comparison the conventional method because it uses semiconducting TiO2 other than electrochemically active materials such as RuO2. The later has been adopted to make electrochemical-double-layer hybrid supercapacitors, however, the former is attributed to a pure double-layer supercapacitor. (C) 2004 Elsevier Ltd. All rights reserved.