A method of ion implantation of a semiconductor devices to neutralize electrostatic charge stored on a wafer. Neutralizing electrons are supplied to a passage through which a positive ion beam is passed while forming a barrier of negative electrostatic potential between an area in the passage to which the neutralizing electrons are supplied and the wafer. When the positive ion beam is not present in the passage, the potential of the barrier is set lower than the negative potential corresponding to energy held in the neutralizing electrons. When the beam is not passed through the passage, most of the neutralizing electrons cannot cross over the barrier, but when the beam is passed through the passage, most of the electrons can cross over the barrier, following it, to shower over the wafer.