Abstract: A wafer bonded CMUT array comprising a plurality of CMUT elements distributed across a substrates, each element comprising a cavity and a signal electrode formed in the substrate, and a conductive membrane closing the cavity and forming a ground electrode, wherein the membranes of the individual elements form an unbroken ground plane across the surface of the array and wherein electrical connection to the signal electrodes is provided by means of a conductive vias depending therefrom through the substrate from the signal electrode to the rear of the substrate.