Capacitance measurements on undoped polycrystalline silicon gate capacitors are used for oxide trapping characterization. In this structure, a field‐effect modulation on both interfaces is observed in a singleC‐Vplot. A variation in the insulator charge state is detected by its effect on both interfaces. The main advantage of this method is that both trapped charge magnitude and centroid are obtained by a single measurement with a minimal disturbance of the charge distribution. The method is demonstrated on thin oxide capacitors subjected to negative or positive charge trapping. The induced positive and negative charge magnitude and location dependence on the injection conditions are measured and analyzed.