Characterization of a n-type Field Effect Transistor (FET) made from direct growth and patterning of a dense single wall carbon nanotubes (SWNTs) network on a silicon substrate, using alcohol as source gas, is presented. This SWNTs network film made into FET has a special feature which is significantly different from the amorphous silicon thin film transistor (TFT) or the MOSFET. The primary n-type nature of the SWNTs FET exhibits ambipolar characteristic. In addition, different sizes of channel for the FET have been made to examine if the scaling law used in TFT or MOSFET applicable. The results found that unlike the mobility of silicon film measured in TFT or MOSFET which do not depend on the size of the channel, both the mobility and the transconductance of the SWNTs film measured in FET increases with the channel width. The current device has an advantage to improve the mobility simply be making a wider channel. More discussions on the characteristics of the SWNTs film FET are provided.