Abstract: Uniform diamond thin films with 3″ diameter were grown by hot filament chemical vapor deposition (HFCVD). Graphite electrodes which were located above the filament were applied, and negative bias relative to the filament were also applied during the nucleation stages. In such case,the diamond nucleation density can reach 10¹⁰~10¹¹/cm². A very uniform diamond film was grown on the mirror-polished ϕ3″ Si wafer. The grown films were characterized by SEM and Raman spectroscopy. The position of electrodes are found to be the very important factor that effect the diamond growth uniformly.