A detailed analysis of the capacitance sensor from a scanning capacitance microscope (SCM) is presented. PSPICE circuit simulations are compared with experimental results. The general behavior of the SCM sensor and practical aspects of the sensor-tuning curve are described. It is found that stray capacitances of the magnitude encountered in a conventional SCM measurement configuration are large enough to significantly decrease measurement sensitivity and sensor high-frequency voltage across the tip sample. We have also calculated and measured the delocalized dC/dV caused by stray capacitance, revealing that this background dC/dV must be accounted for in order to obtain the true localized dC/dV. (C) 2004 American Vacuum Society.