Wang, Y.W. Adderley, P.A. Benesch, J. F. Bullard, D.B. Grames, J.M. Hannon, F.E. Hansknecht, J. Hernandez-Garcia, C. Kazimi, R. Krafft, G.A. Mamun, M.A. Palacios Serrano, G.G. Poelker, M. Suleiman, R. Tiefenback, M.G. Wijethunga, S.A.K. Zhang, S. JACoW Publishing Geneva, Switzerland 978-3-95450-184-7 10.18429/JACoW-IPAC2018-THPMK110 English 4571-4574 THPMK110 Contribution to a conference proceedings 2018 2018-06 https://doi.org/10.18429/JACoW-IPAC2018-THPMK110 http://jacow.org/ipac2018/papers/thpmk110.pdf A compact DC high voltage photogun with inverted-insulator geometry was designed, built and operated reliably at 300 kV bias voltage using alkali-antimonide photocathodes. This presentation describes key electrostatic design features of the photogun with accompanying emittance measurements obtained across the entire photocathode surface that speak to field non-uniformity within the cathode/anode gap. A summary of initial photocathode lifetime measurements at beam currents up to 4.5 mA is also presented.