The hot-carrier reliability of 12 V high-voltage n-channel double diffused drain metal-oxide-semiconductor (DDDMOS) field-effect transistors with various n-type double diffusion (NDD) implant dosages is investigated. A high NDD implant dosage results in a high substrate current; however, on-resistance (R on ) degradation is low. The damage location shifting toward the channel is responsible for this unexpected low R on degradation. Technology computer-aided design (TCAD) simulation and charge pumping measurements are carried out to identify the damage location. Our analysis results reveal that an increase in NDD dosage is effective for improving the reliability of the DDDMOS field-effect transistors.