This article describes experimental measurements and computer calculations of the location of microtrenches in the gate oxide at the periphery of a complementary metal-oxide semiconductor gate resulting from a polysilicon gate etch with a low pressure, high density plasma, etch tool. When the oxide is removed at the periphery of a gate with the etch process, it is possible to damage the underlying silicon in the source and drain regions. This damage may not be observable in scanning electron microscope pictures but could still lead to device degradation or failure. To measure the integrity of the oxide at the gate periphery, a modified MOS (MMOS) capacitor test structure was used to measure the electric field breakdown strength of the oxide at the gate periphery. The breakdown voltage can be related to the amount of remaining oxide at the gate periphery. This article describes the use of the MMOS test structure to measure the location of the microtrenches relative to the gate edge in a low pressure, high density plasma, polysilicon gate etch tool.