A low on-resistance (Ron, sp) integrable silicon-on-insulator (SOI) n-channel lateral double-diffused metal-oxide- semiconductor (LDMOS) is proposed and its mechanism is investigated by simulation. The LDMOS has two features: the integration of a planar gate and an extended trench gate (double gates (DGs)); and a buried P-layer in the N-drift region, which forms a triple reduced surface field (RESURF) (TR) structure. The triple RESURF not only modulates the electric field distribution, but also increases N-drift doping, resulting in a reduced specific on-resistance (Ron, sp) and an improved breakdown voltage (BV) in the off-state. The DGs form dual conduction channels and, moreover, the extended trench gate widens the vertical conduction area, both of which further reduce the Ron, sp. The BV and Ron, sp are 328 V and 8.8 m&ohmega;.cm2, respectively, for a DG TR metal-oxide-semiconductor field-effect transistor (MOSFET) by simulation. Compared with a conventional SOI LDMOS, a DG TR MOSFET with the same dimensional device parameters as those of the DG TR MOSFET reduces Ron, sp by 59% and increases BV by 6%. The extended trench gate synchronously acts as an isolation trench between the high-voltage device and low-voltage circuitry in a high-voltage integrated circuit, thereby saving the chip area and simplifying the fabrication processes. [ABSTRACT FROM AUTHOR]