A structure for protecting a semiconductor circuit from electrostatic discharge is provided. The structure comprises a semiconductor substrate of a first conductivity type having two wells of a second conductivity type spaced laterally apart. The wells each comprise a first portion having a first concentration of an impurity of the second conductivity type and a second portion comprising source and drain regions having a second concentration of an impurity of the second conductivity type. The second concentration is greater than the first concentration. The wells are implanted in the substrate of a silicon-on-insulator semiconductor device. Conductive plugs extend through the silicon and insulator layers and make electrical contact with the wells, allowing the dissipation of excess current and heat into the semiconductor substrate.