The work function of W(100) surface is successfully reduced to 2.0 eV. Y2O3 fine powder is attached to the shank of a sharp W(100) needle and heat treated in a vacuum of 10(-7) Pa. The emission pattern has a fourfold symmetry with a bright center spot. The work function is estimated with the aid of a Fowler-Nordheim plot. The reduced rate of work function is fairly coincident with the prediction done by Saito et al. (unpublished) and also by Nishiyama, Ohshima, and Shinada [Appl. Surf. Sci. 146, 382 (1999)]. These researchers predicted the reducing rate is proportional to the product of difference of the electronegativities and sum of the ionic radii of the metal atom and oxygen. (C) 2004 American Vacuum Society.