The vertically aligned multiwalled carbon nanotubes (CNT) are synthesized in high density on a large area of cobalt deposited silicon oxide substrate, by thermal chemical vapor deposition using C2H2 gas, at 950 degrees C. The diameter of CNTs is distributed in the range of 80-120 nm and the length is about 20 mu m. High-resolution transmission electron microscopy analysis reveals that the multiwalled CNTs have the crystalline graphite sheets and the bamboo structure that the tube consists of hollow compartments separated with graphite layers. A possible growth mechanism is suggested to explain the structure of CNTs. The emission current density is 1.1 mA cm(-2) at 4.5 V mu m(-1), showing the Fowler-Nordheim behavior.