The carbon nanotube field-effect transistor (CNTFET) is a promising candidate for future electronic devices. Numerical studies are performed to investigate the impact of structural and process parameters on the conventional CNTFETs. The impact of channel length, gate dielectric thickness and permittivity, source/drain dopant concentration, workfunction of the gate, and drain voltage are studied. The drain current of the transistor increases as the nanotube diameter increases or as the gate workfunction decreases. The transistor current is almost independent of source/drain dopant concentration at high dopant densities. But at low dopant concentrations it increases as dopant density increases.