An integrated circuit is formed on a substrate containing a semiconductor material having a first conductivity type. A deep well having a second, opposite, conductivity type is formed in the semiconductor material of the first conductivity type. A deep isolation trench is formed in the substrate through the deep well so as separate an unused portion of the deep well from a functional portion of the deep well. The functional portion of the deep well contains an active circuit element of the integrated circuit. The separated portion of the deep well does not contain an active circuit element. A contact region having the second conductivity type and a higher average doping density than the deep well is formed in the separated portion of the deep well. The contact region is connected to a voltage terminal of the integrated circuit.