Junction leakage current from two depletion layers, a depletion layer (8) in the well and a depletion layer (4) at the interface between the EP layer (2) and the EP substrate (1), is measured.

An insulated gate (16) controls the position and thickness of the depletion layer.

In an off-state of the device, the body portion (16) carries a depletion layer (50).

A specific layer is disposed on a bottom of the trench, and it has a characteristic of forming a depletion layer at a junction between the specific layer and the drift region.

The transducer is found to be active only in the vicinty of one of the two boundary layers as a result of the presence of a depletion layer and an accumulation layer, which in any case only extend in the vicinity of one of the boundary surfaces.