Normally-off heterojunction integrated device and method for manufacturing an integrated device

An integrated power device includes a heterostructure, having a channel layer and a barrier layer, a source contact, a drain contact, and a gate region, arranged on the barrier layer between the source contact and the drain contact. An insulating field structure is arranged on the barrier layer between the gate region and the drain contact. A field plate extends over the insulating field structure. The insulating field structure includes a first dielectric region made of a first dielectric material on the barrier layer and a second dielectric region made of a second dielectric material, selectively etchable with respect to the first dielectric material on the first dielectric region. On a side of the insulating field structure towards the gate region, the field plate is in contact with the first dielectric region.