An acoustic microelectronic device includes a support, a set of at least one membrane suspended on a face of the support above a cavity by an anchoring zone, and at least one acoustic insulation trench arranged adjacent to the membrane. The device includes at least one bridge connecting the portions of two opposite edges of the trench and located overhanging at least one zone of the trench so as to form, in the zone of the trench, an acoustic insulation box below the bridge.