Disclosed is a method of manufacturing a capacitive micro-machined ultrasonic transducer (CMUT) device comprising a first electrode (112) on a substrate (110) and a second electrode (122) embedded in an electrically insulating membrane, the first electrode and the membrane being separated by a cavity (130) formed by the removal of a sacrificial material (116) in between the first electrode and the membrane, the method comprising forming a membrane portion (22) on the second electrode and a further membrane portion (24) extending from the membrane portion towards the substrate alongside the sacrificial material, wherein the respective thicknesses the membrane portion and the further membrane portion exceed the thickness of the sacrificial material prior to forming said cavity. A CMUT device manufactured in accordance with this method and an apparatus comprising such a CMUT device are also disclosed.