An enhanced leakage current through thin SiO2gate insulators following ion implantation of source/drain regions in self‐aligned gate complementary‐metal‐oxide semiconductors has been examined. The enhanced leakage current degrades insulator properties and is localized at the perimeter of the gate feature. A model of ion mixing between the gate material, oxide layer, and underlying silicon at the gate‐feature edge has been used to explain the degradation. The atomic weight of the implant species is critical, with heavier species like arsenic demonstrating a severe degree of degradation. Implantation of lighter species like boron results in minimal degradation at normal dose levels. The gate‐electrode material is also important. Electrodes formed with the highest‐atomic‐weight and density materials demonstrate the most degradation. Gate charging during the ion‐implantation process does not significantly impact the degree to which samples are degraded at the implant currents used in this work.