The material and electrical properties of the CNT single vias and array vias grown by microwave plasma-enhanced chemical vapor deposition were investigated. The diameters of multiwall carbon nanotubes (MWNTs) grown on the bottom electrode of Ta decrease with increasing pretreatment power and substrate temperature while the effects of the growth power and methane flow ratio are insignificant The decrease of CNT diameters leads to the decrease of the CNT via diode devices. The increase of growth power enhances the CNT graphitization degree and thue the conductivity of CNT via diode devices. In the same via region, the MWNT diode resistances of the array vias are lower than those of the single vias. The MWNT diode resistances on the bottom electrode of titanium are lower than those on the bottom electrode of tantalum. It may be attributed to the smaller tube diameters on the bottom electrode of Ti and the work function difference between Ta and Ti films with respect to the work function of CNTs.