Abstract: Highly boron-doped diamond (BDD) films were deposited by hot filament chemical vapor deposition on a silicon substrate with different gas pressures and bias currents. The surface morphology and the structure of the diamond films were analyzed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Results indicated that the quality of the highly BDD films tended to be improved when the gas pressure decreased from 3 to 1. 5kPa, whereas they showed an opposite trend with a further decrease of the gas pressure from 1. 5 to 0. 5 kPa. An appropriate bias current (3A) was favorable in improving the qualities of the diamond films and a higher bias current led to an increase of the non-diamond phase in the films.