An improved vertical power double-diffused metal–oxide–semiconductor (DMOS) device with a p-region(P1) and high-κ insulator vertical double-diffusion metal–oxide–semiconductor (HKP-VDMOS) is proposed to achieve a better performance on breakdown voltage (BV)/specific on-resistance (Ron,sp) than conventional VDMOS with a high-κinsulator (CHK-VDMOS). The main mechanism is that with the introduction of the P-region, an extra electric field peak is generated in the drift region of HKP-VDMOS to enhance the breakdown voltage. Due to the assisted depletion effect of this p-region, the specific on-resistance of the device could be reduced because of the high doping density of the N-type drift region. Meanwhile, based on the superposition of the depleted charges, a closed-form model for electric field/breakdown voltage is generally derived, which is in good agreement with the simulation result within 10％of error. An HKP-VDMOS device with a breakdown voltage of 600 V, a reduced specific on-resistance of 11.5 m?·cm2 and a figure of merit (FOM) (BV2/Ron,sp) of 31.2 MW·cm?2 shows a substantial improvement compared with the CHK-VDMOS device.