Effects of drift-region design on the hot-carrier reliability of n-channel integrated high-voltage lateral diffused MOS (LDMOS) transistors are investigated. LDMOS devices with various dosages of n-type drain drift (NDD) implant and various drift-region lengths (Ld) are studied. Results show that higher NDD dosage can reduce hot-carrier induced on-resistance (R on) degradation. The shift in damage location is suggested to be the main cause. In addition, longer Ld can reduce Ron degradation significantly because of less lateral electric field. Our analysis indicates that higher NDD dosage and longer Ld are effective for improving the device lifetime of the LDMOS transistors.