A pressure-sensitive switch comprises a base member having a mounting surface formed of electrically-insulating material; two electrodes mounted on the base member and each having an electrically-conductive contact surface, and a flexible diaphragm having its periphery secured in a fluid-tight manner to the mounting surface with its electrically-conductive central portion overlying the contact surfaces of the electrodes. The diaphragm, which is formed with plural corrugations, is exposed to the external pressure. When the switch is exposed to atmospheric pressure, the central portion of the diaphragm does not touch the contact surfaces of said electrodes, but when the switch is exposed to a super-atmospheric pressure, this central portion is forced into contact with both contact surfaces, thus electrically connecting the two electrodes. This pressure-sensitive switch is especially useful for use with hydrophones, as in seismic streamer cables.