A new partial SOI (silion-on-insulator) (PSOI) high voltage P-channel LDMOS (lateral double-diffused metal-oxide semiconductor) with an interface hole islands (HI) layer is proposed and its breakdown characteristics are investigated theoretically. A high concentration of charges accumulate on the interface, whose density changes with the negative drain voltage, which increase the electric field (E I ) in the dielectric buried oxide layer (BOX) and modulate the electric field in drift region . This results in the enhancement of the breakdown voltage (BV). The values of E I and BV of an HI PSOI with a 2-μm thick SOI layer over a 1-μm thick buried layer are 580V/μm and 582 V, respectively, compared with 81.5 V/μm and 123 V of a conventional PSOI. Furthermore, the Si window also alleviates the self-heating effect (SHE). Moreover, in comparison with the conventional device, the proposed device exhibits low on-resistance. A new partial SOI (silion-on-insulator) (PSOI) high voltage P-channel LDMOS (lateral double-diffused metal-oxide semiconductor) with an interface hole islands (HI) layer is proposed and its breakdown characteristics are investigated theoretically. A high concentration of charges accumulate on the interface, whose density changes with the negative drain voltage, which increase the electric field (EI) in the dielectric buried oxide layer (BOX) and modulate the electric field in drift region. the breakdown of voltage (BV). The values ​​of EI and BV of an HI PSOI with a 2-μm thick SOI layer over a 1-μm thick buried layer are 580V / μm and 582 V, respectively, compared with 81.5 V / μm and 123, of the conventional PSOI. Furthermore, the Si window also alleviates the self-heating effect (SHE). Moreover, in comparison with the conventional device, the proposed device exhibits low on-resistance.