The hot-carrier reliability of a 700 V n-LDMOS transistor under different stress conditions is investigated in detail. For the high drain voltage (V ds ) condition, the degradation of the saturate drain current (I dsat ) is different from the on-resistance (R on ) degradation for the change of the dominated degradation mechanism. Moreover, the serious R on degradation has identical variation tendency with substrate current (I sub ) because the maximum impact ionization occurs at the surface of the drift region. However, for the high gate voltage (V gs ) condition, the most important degradation is the threshold voltage (V th ). We found that the V th degradation has an exponential relationship with V gs . In addition, it is also observed that the thick field oxide results in strong and rapid recovery of the R on degradation.