The invented ink-jet printing method for the construction of thin film transistors using all SWNTs on flexible plastic films is a new process. This method is more practical than all of existing printing methods in the construction TFT and RFID tags because SWNTs have superior properties of both electrical and mechanical over organic conducting oligomers and polymers which are often used for TFT. Furthermore, this method can be applied on thin films such as paper and plastic films while silicon based techniques cannot be used on such flexible films. These are superior to the traditional conducting polymers used in printable devices since they need no dopant and they are more stable. They could be used in conjunction with conducting polymers, or as stand-alone inks.