We have demonstrated the fabrication of horizontally aligned carbon nanotube (CNT) bundles on Si substrate for interconnect line application. By controlling the catalyst thickness, we fabricated multi-walled CNT and few-walled CNT bundles with different diameters. We measured the resistances of the CNTs as a function of the length and the diameter. The dependence of the contact resistance between the CNT and the metal on the CNT diameter was extracted from the resistance plots. We investigated and experimentally validated the relationship between the diameter and the mean free path of the CNT.