Metal-catalyzed nanowires have previously been proposed as the active elements of field-effect devices, such as metal oxide field effect transistors and sensors. For these applications, the nanowire surface properties must be understood and controlled. Initial measurements of nanowire surface-charge density are presented here. The surface-charge density was obtained by measuring nanowires of different diameters grown between electrodes. The surface-charge density of a nanowire covered with native oxide is about 2 x 10(12) cm(-2); the density appears to decrease by a factor of two to four when the native oxide is replaced by a high-quality thermally grown oxide, with further improvement possible. (c) 2006 The Electrochemical Society.