The thermal conductivity of as-grown vertical multi-walled carbon nanotubes (CNT) bundles fabricated at low temperature (500?°C) was measured using a vertical 3?-method. For this, CNT were selectively grown inside an oxide opening and sandwiched between two metal electrodes. The validity of the method was confirmed by both measurements as simulations. The measured thermal conductivity of 1.7-3.5?W/mK is significantly lower than values reported before, which is caused by the low quality of the tubes. This clearly indicates that tube quality will be essential when integrating CNT.