Diamond was grown on polycrystalline CoSi2/Si substrates by bias-enhanced microwave plasma chemical vapor deposition. Both of the positive and negative biasing effects were investigated by microstructural characterization. It has been found that nucleation density can reach similar to 10(9) cm(-2) with positive biasing, much higher than with negative biasing. Cross-sectional transmission electron microscopy shows that diamond deposited by positive biasing grows on a relatively smooth CoSi2 surface, while the etching effect of ion bombardment during negative biasing results in a rough CoSi2 surface. The diamond morphology obtained with negative bias has a flat surface with a strong (1 0 0) texture.