Many molecular beam epitaxy (MBE) applications require a source of ionized gas atoms or molecules. However, the high gas pressures and high kinetic energies associated with many standard gas sources can be detrimental to MBE deposition. These disadvantages are addressed here by an ionized gas source fabricated from a common laboratory ionization gauge. The source described here produces 100 eV gas ions while maintaining vacuums of better than10−8 mbar.This source has the additional advantage of being inexpensive and simple to construct. Design, construction, and operation of the source will be presented. ©1997 American Institute of Physics.