We have fabricated an array of cone-shaped diamond tips for use as a field electron emitter by air-plasma etching a polycrystalline diamond film with a silicon oxide mask. The difference in etching speed between the mask and the diamond resulted in the formation of cone-shaped diamond tips. Post-treatment with hydrogen plasma was effective in cleaning the diamond tips and increasing the surface conductivity. The emission from the diamond tips was measured with a diode configuration. The threshold field was 3Vμm - 1 , and the emission current was 0.8nAtip - 1 when the field was raised to 10Vμm - 1 .