An extreme high vacuum field emission microscope (XHV FEM) was constructed for the study of inherent fluctuations of field emission (FE) current. The damping and fluctuation behaviors of FE current from clean W(l 11) tips at 90 K were observed using the XHV FEM. Exposure to XHV of 7.5 x 10(-10) Pa continued to damp FE current for more than 2000 min. The fluctuation (similar to 0.01 %) of FE current (1 nA) for the clean W(111) tips was comparable to the corresponding shot noise fluctuation (0.005%), demonstrating the suitability of the XHV FEM for the inherent fluctuation study of the FE process. After saturating the tip surface with hydrogen, the FE current showed fluctuations of <0.1%. (C) 2007 American Vacuum Society.