Abstract: An electronic power device is integrated monolithically in a semiconductor substrate. The device has a first power region and a second region, each region comprising at least one P/N junction formed of a first semiconductor region with a first type of conductivity, which first semiconductor region extends through the substrate from the top surface of the device and is diffused into a second semiconductor region with the opposite conductivity from the first. The device also includes an interface structure between the two regions, of substantial thickness and limited planar size, comprising at least one trench filled with dielectric material.