The need for a high performance (low energy spread < 0.5 eV. long lifetime > 3 months per spot, emission stability < 1% /h) electron source continues as part of the development of new e-beam writing and inspection tools. We present measurements from a group III-nitride (indium gallium nitride) photocathode in a demountable vacuum system to measure energy spread. lifetime. and preliminary blanking effects. We show the results of cathodes operating in ultrahigh vacuum (UHV), high vacuum (HV), and oxygen-rich backpressures. Our results show InGaN has a longitudinal energy spread of <300 meV in reflection mode, flat lifetimes of 60 h per illuminated spot where the yield changes by <10%, and stable emission with typical recoveries within 99% of original photocurrent for all blanking periods and vacuum conditions tested (0.5 to 10 min periods). (C) 2004 American Vacuum Society.