We carried out two-dimensional numerical calculations of electrostatic potential for triode field emitters with planar cathodes using the finite-element method. As it turned out, the conventional triode structure with a planar cathode suffered from large gate current and wide spreading of emitted electrons. To circumvent these shortcomings, we proposed another triode structure. By simply inserting a conducting layer of proper thickness between the gate insulator and the cathode layer, we were able to modify the electric-field distribution on the cathode surface so that low gate current and electron-focusing effect were achieved, simultaneously. (C) 2003 American Vacuum Society.