Direct growth of 100 mm long, semiconducting triple-walled carbon nanotubes (TWNTs) on Si substrates by chemical vapor depoistion is reported. By tailoring the temperature for a certain gas flow rate, a yield of nearly 90% of centimeter-long TWNTs is obtained. The TWNTs show an unprecedented structural homogeneity, in which each shell maintains a constant chiral index extending over a very large distance (>60 mm). The semiconducting TWNTs can be directly fabricated into field-effect transistors.