Breakdown voltage BVdss is enhanced and ON-resistance reduced in RESURF devices, e.g., LDMOS transistors, by careful charge balancing, even when body and drift region charge balance is not ideal, by: (i) providing a plug or sinker near the drain and of the same conductivity type extending through the drift region at least into the underlying body region, and/or (ii) applying bias Viso to a surrounding lateral doped isolation wall coupled to the device buried layer, and/or (iii) providing a variable resistance bridge between the isolation wall and the drift region. The bridge may be a FET whose source-drain couple the isolation wall and drift region and whose gate receives control voltage Vc, or a resistor whose cross-section (X, Y, Z) affects its resistance and pinch-off, to set the percentage of drain voltage coupled to the buried layer via the isolation wall.