Carbon nanotube (CNT) is a promising candidate for transistor and interconnects for nanoelectronic circuits. Although CNT intrinsically has excellent electrical conductivity, the large contact resistance at the interface between CNT and metal hinders its practical application. Here we show that the electrical contact to CNT is substantially improved using a graphitic interfacial layer catalyzed by a Ni layer. The p-type semiconducting CNT with graphitic contact exhibits high ON-state conductance at room temperature, and steep sub-threshold swing with back-gate configuration. We also show the contact improvement to semiconducting CNT with different capping metals. To study the role of the graphitic interfacial layer in the contact stack, the capping metal and Ni catalyst were selectively removed, and replaced with new metal pads deposited by evaporation and without further annealing. Good electrical contact to semiconducting CNT was still preserved after the new metal replacement, indicating that the contact improvement is attributed to the presence of the graphitic interfacial layer.