A RESURF-enhanced high voltage SOI LDMOS(ER-LDMOS) with an ultralow specific on-resistance(R_(on,sp)) is proposed.The device features an oxide trench in the drift region,a P-pillar at the sidewall of the trench,and a buried P-layer(BPL) under the trench.First,the P-pillar adjacent to the P-body not only acts as a vertical junction termination extension(JTE),but also forms a vertical reduced surface field(RESURF) structure with the Ndrift region.Both of them optimize the bulk electric field distributions and increase the doping concentration of the drift region.Second,the BPL together with the N-drift region and the buried oxide layer(BOX) exhibits a tripleRESURF effect,which further improves the bulk field distributions and the doping concentration.Additionally,multiple-directional depletion is induced owing to the P-pillar,the BPL,and two MIS-like structures consisting of the N-drift region combined with the oxide trench and the BOX.As a result,a significantly enhanced-RESURF effect is achieved,leading to a high breakdown voltage(BV) and a low R_(on,sp).Moreover,the oxide trench folds the drift region in the vertical direction,resulting in a reduced cell pitch and thus R_(on,sp) Simulated results show that the ER-LDMOS improves BV by 67% and reduces R_(on,sp) by 91% compared with the conventional trench LDMOS at the same cell pitch. A RESURF-enhanced high voltage SOI LDMOS (ER-LDMOS) with an ultralow specific on-resistance (R_ (on, sp)) is proposed. The device features an oxide trench in the drift region, a P-pillar at the sidewall of the trench, and a buried P-layer (BPL) under the trench. First, the P-pillar adjacent to the P-body not only acts as a vertical junction termination extension (JTE) RESURF) structure with the Ndrift region. Both of them optimize the bulk electric field distributions and increase the doping concentration of the drift region. Second, the BPL together with the N-drift region and the buried oxide layer (BOX) exhibits a triple RESURF effect , which further improves the bulk field distributions and the doping concentration. Additionally, multiple-directional depletion is induced due to the P-pillar, the BPL, and two MIS-like structures consisting of the N-drift region combined with the oxide trench and the BOX.As a result, a significantly enhanced-RESURF effect i leading to a high breakdown voltage (BV) and a low R_ (on, sp) .Moreover, the oxide trench folds the drift region in the vertical direction, resulting in a reduced cell pitch and thus R_ (on, sp) Simulated results show that the ER-LDMOS improves BV by 67% and reduces R_ (on, sp) by 91% compared with the conventional trench LDMOS at the same cell pitch.