A device for detecting magnetic fields, of the type comprising at least one element made of hard 5 magnetic material (12) and an element made of soft magnetic material (13) associated an element made of semiconductor material (11), electrodes (15) for forcing a current (I) in the semiconductor material (11), characterised in that the element made of hard magnetic material (12) and element made of soft magnetic material (13) are positioned in planar fashion on the element made of semiconductor material (11).