For the first time, a new drain-bias TBD lifetime model is proposed to precisely predict at various Vd, Vg and channel length for ultra thin oxide. The TBD lifetime with drain-bias can be decoupled to small voltage drop at drain-side increased TBD lifetime and hot carrier effect (HCI) degraded the TBD lifetime. The mechanism of oxide breakdown with drain-bias is also well understood as oxide traps distributed from the source side to the center of channel induce the oxide breakdown.