Glycines are spontaneously adsorbed to form into self-assembled nanoclutsers on single-walled carbon nanotubes (SWNTs). After formation of glycine nanoclusters on SWNTs, the field effect transistor (FET) devices show selective sensing ability to alcohols, such as isopropyl alcohol (IPA), methanol, and ethanol. Upon the adsorption of alcohol, the glycine-coated SWNT-FET devices exhibit pseudo-metallic transport behaviors, whereas the original and glycine-coated devices display conventional p-type transport characteristics. Computational studies support that the gate field screening effect induced by instantly formed glycine-alcohol pair layers seems to be responsible for the pseudo-metallic transport behavior.