Carbon nanotubes (CNTs) arc grown on Ni catalysts employing an inductively-coupled plasma chemical vapor deposition (ICP-CVD) method. The structural and field-emissive properties of the CNTs grown are characterized in terms of the substrate-bias applied. Characterization using the various techniques, such as field-omission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Auger spectroscopy (AES), and Raman spectroscopy, shows that the structural properties of the CNTs, including their physical dimensions and crystal qualities, as well as the nature of vertical growth, are strongly dependent upon the application of substrate bias during CNT growth. It is for the first time observed that the provailing growth mechanism of CNTs, which is either due to tip-driven growth or based-on-catalyst growth, may be influenced by substrate biasing. It is also seen that negatively substrate-biasing would promote the vertical-alignment of the CNTs grown, compared to positively substrate-biasing. However, the CNTs grown under the positively-biased condition display a higher electron-emission capability than those grown under the negatively-biased condition or without any bias applied.