An ionisation vacuum gauge for measuring the residual pressure of a gaseous material remaining in a container (10), more particularly after operation of a vacuum pump comprises an electron-emitting cathode (31) made by exploiting the nanotube technology, a grid (13; 33; 133; 133′) for accelerating the electrons emitted by the cathode, and a plate (15; 35) collecting the ions and/or the ionised positive molecules of the gas. Measuring the plate current by a galvanometer allows for determining the value of the residual pressure inside the container.