Here, we reveal origins of the planar electrical transport of closely-packed carbon nanotubes (CNTs) and silicon-doped CNTs (Si-CNTs) films. Their electrical resistivities increased with decreasing temperature, but exhibit a plateau below 60 K. This phenomenon can be well described using the simple-two-band model, which is often used to understand the electronic properties of graphite. Cryogenic energy-filtered transmission electron microscopy visualizes Si atoms dispersed finely in CNTs, preserving the structural features of CNTs. These Si atoms induced effective carriers above 150 K, while three-dimensional variable range hopping and weak localization are dominant in their transport below 50 and 10 K, respectively. (C) 2012 The Japan Society of Applied Physics