The electrical transport and NH3 sensing properties of randomly oriented and aligned SWNT networks were presented and discussed. The results indicate that aligned SWNT-FETs have better FET characteristics due to the reduced number of interconnected nodes. This was particularly true as the resistance of the devices increased. Gated electrical breakdown was implemented to selectively remove metallic (m-) SWNTs, thereby reducing scattering centers. This technique provided significant improvements in FET characteristics resulting in greater on/off ratio (e.g. 104). AC dielectrophoretic alignment followed by selective electrical breakdown of m-SWNTs can significantly enhance the semiconducting properties of SWNT networks which resulted in highly sensitive sensors. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.