Well-aligned carbon nanotubes (CNTs) have been grown on nickel-deposited silicon wafers by thermal chemical vapor deposition (CVD) of ethylenediamine precursor. The CNTs are vertically aligned at high density over large areas on the silicon surface. The size and the density of the nanotubes were found to be dependent on the thickness of the Ni film. The length of the nanotube array can be controlled by varying the CVD time. High-resolution transmission electron microscopy analysis revealed that the CNTs present bamboo-like multi-walled structure.