Nishimori, N. MOD01 gun cathode emittance FEL brightness 2015 2015-12 Future ERL light sources and high repetition rate X-ray FELs require high-brightness and high-current electron guns. A DC photoemission gun is one of the most promising candidates for such guns, because a record high current of 65 mA and generation of high brightness beam with 90% normalized emittances of 0.3 mm-mrad with bunch charge of 77 pC were recently demonstrated at the Cornell photoinjector with a 350 kV photoemission gun [1,2]. Further increase of the gun high voltage is desirable to reduce space charge induced emittance growth especially for high bunch charge application such as X-ray FEL. Employment of a segmented insulator is a key to reach higher voltage [3]. This technique led to generation of 500 keV beam from the JAEA gun with 160mm acceleration gap [4], conditioning voltage more than 500 kV at the Cornell gun with gap < 50 mm [5], and demonstration of 500 kV holding for 10 hours at the KEK gun with 70 mm gap [6]. In this talk, we present recent experimental results of high brightness DC guns and discuss highlights and limitations in FEL applications.