A new structure of RESURF LDMOSFET is proposed, based on silicon-on-insulator, to improve the characteristics of the breakdown voltage and the specific on-resistance, where a trench is applied under the gate in the drift region. A trench is used to reduce the electric field under the gate when the concentration of the drift region is high, thereby increasing the breakdown voltage and reducing the specific on-resistance. Detailed numerical simulations demonstrate the characteristics of this device and indicate an enhancement on the performance of the breakdown voltage and the specific on-resistance in comparison with an optimal conventional device with LOCOS under the gate. (C) 2004 Elsevier Ltd. All rights reserved.