A movable mass forming a seismic mass is formed starting from an epitaxial layer and is covered by a weighting region of tungsten which has high density. To manufacture the mass, buried conductive regions are formed in the substrate. Then, at the same time, a sacrificial region is formed in the zone where the movable mass is to be formed and oxide insulating regions are formed on the buried conductive regions so as to partially cover them. An epitaxial layer is then grown, using a nucleus region. A tungsten layer is deposited and defined and, using a silicon carbide layer as mask, the suspended structure is defined. Finally, the sacrificial region is removed, forming an air gap.