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In order to achieve a high breakdown voltage (BV) and to avoid local breakdown in high-voltage integrated circuits, a novel double-well (DW) high-voltage divided reduced surface field (RESURF) isolation structure featuring two slender N-well regions located at N--well region is proposed for the first time. The breakdown mechanisms are investigated by theoretical analysis and experimental measurements. In the high-voltage blocking state, the N-well regions can efficiently prevent the P-well region from depleting with the high-side region, so as to maintain the charge balance of the novel isolation structure, which leads to an increase in the BV from 656 V in the conventional isolation structure to 760 V in the proposed structure. The dependence of the electrical characteristics of the isolation on the structure parameters has been analyzed in detail. The novel DW divided RESURF structure has been fabricated in 0.5- μm bipolar-CMOS-DMOS technology, which has verified the feasibility and validity of the new concept.