This work examines the electron emission characteristics of a polycrystalline diamond-coated silicon field emitter fabricated by hot filament chemical vapor deposition. The electron emission behavior of a polycrystalline diamond-coated Si field emission array (D/Si-FEA) was compared with that of an uncoated Si field emission array (SI-FEA) and flat-diamond film coated on Si substrate (flat-D/Si). From Raman spectrum and x-ray diffraction pattern analyses, it was revealed that the overcoated diamond film involved structural defects, graphite inclusion, grain boundaries, and a negative electron affinity surface. The direct current current-voltage (I-V) characteristics exhibited linear ohmic emission behavior at low anode voltages and Fowler-Nordheim emission behavior at high anode voltages. The threshold voltages for the D/Si-FEA, Si-FEA, and flat-D/Si were about 250, 666, and 800 V, respectively. The maximum emission current for the D/Si-FEA, 0.23 mA, was obtained for a 500 V anode bias. The low onset voltage of the D/Si-FEA was attributed to the cone-shaped emitter and the excellent properties of the overcoated diamond film.