Abstract: An ion source suitably used for an etching process among manufacturing processes for e.g. semiconductor devices, comprising a vacuum container, an anode disposed in the vacuum container, a cathode having one or more looped slits formed opposite said anode, and one or more permanent magnets located in a position or positions corresponding to a portion of the cathode surrounded by the looped slit or slits and forming a magnetic field having a direction at substantially right angles to the direction of an electric field formed by applying a voltage between the anode and cathode, a gas which is introduced into the vacuum container through an inlet means formed in the vacuum container being made into gas plasma by means of the electric and magnetic fields at right angles to each other, whereby positive ions in the gas plasma will be taken out through the looped slit or slits.