We have grown vertically aligned carbon nanotubes on a large area of Co-Ni codeposited Si substrates by thermal chemical vapor deposition using C2H2 gas. The carbon nanotubes grown by the thermal chemical vapor deposition are multi-wall structure, and the wall surface of nanotubes is covered with defective graphite sheets or carbonaceous particles. The carbon nanotubes range from 50 to 120 nm in diameter and about 130 μm in length at 950 °C. Steric hindrance between nanotubes at an initial stage of the growth forces nanotubes to align vertically. The turn-on voltage was about 0.8 V/μm with a current density of 0.1 μA/cm2 and emission current reveals the Fowler-Nordheim mode.