A fiber-optic pressure sensor apparatus includes a section of optical fiber coupled to an interferometer sensor tip having a structure made almost entirely of silicon. The tip structure includes a thin diaphragm bonded to a tip body. The tip body is bell-shaped in a sectional view and includes a curved cross-sectional shape and includes a fiber grip portion which holds a distal end of the optical fiber and a diaphragm support portion to which is bonded the diaphragm. The diaphragm includes a reflective film which is separated from an end surface of the optical fiber to define an interference cavity. The diaphragm deforms or deflects in response to a pressure difference from one side to the other. The movement of the diaphragm alters the optical path length of the interference cavity. The combination of reflections from the two surfaces of the interference cavity provides a standard optical interference signal for measurement by a measurement apparatus.