Nanoscale electronic devices made from carbon nanotubes (CNTs) such as transistors and sensors are much smaller and potentially more versatile than those built using conventional IC technology. In this paper, we present a method that uses dielectrophoretic (DEP) manipulation process for the fabrication of single-channel and multi-channel carbon nanotube field effect transistors (CNT-FETs). For a typical fabrication process, single-walled carbon nanotubes (SWCNTs) are first pre-aligned to micron-precision range between two microelectrodes using DEP technique. The typically applied alternating current (AC) voltage to generate the DEP force for manipulation has a frequency of 1 MHz and amplitude of 10 V. We first demonstrated single-channel or multi-channel structures of CNT-FETs. An AFM is then used to "clean" or "sweep away" unwanted particles or CNTs around the electrodes. Lastly, the fabricated FETs were covered in a polymethylmethacrylate (PMMA) thin film and treated with an annealing process. The PMMA covered devices show improved performances over the non-covered devices.