A field emission backlight unit includes: upper substrate and lower substrate separated from each other and facing each other; an anode formed on a bottom surface of the upper substrate; a phosphor layer formed on a bottom surface of the anode; a plurality of cathodes and gate electrodes alternately formed on a top surface of the lower substrate; and emitters formed on the cathodes; the gate electrodes include first gate electrodes formed of a conductive material on the top surface of the lower substrate and second gate electrodes having a greater thickness than that of the first gate electrodes and formed on a top surface of the first gate electrodes.