The present invention relates to a capacitive micro-machined ultrasound transducer (CMUT) device (1) for transmitting and/or receiving ultrasound waves, comprising at least one CMUT cell (10). The CMUT cell (10) comprises a substrate (13) comprising a first electrode (22), a membrane (15) comprising a second electrode (20), at least one dielectric layer (21, 23) between the first electrode (22) and the second electrode (20), and a cavity (18) formed between the substrate (13) and the membrane (15). The CMUT device (1) further comprises an operating bias voltage source (25) for supplying an operating bias voltage (VB) of a first polarity between the first and second electrode (20, 22) during transmitting and/or receiving ultrasound waves, and a charging voltage source (30) for supplying an additional charging voltage (VC) between the first and second electrode (20, 22), the second polarity being the reverse polarity of the first polarity. The present invention further relates to a method of operating such a CMUT device.
