Provided is a field-effect transistor (10) which comprises a metal or carbon source electrode (14) and a layer of a functional organic semiconductor (28). A column of an injection material (48) extends through the layer of the functional organic semiconductor (28), the column being in contact with both the source electrode (14) and the layer of the functional organic semiconductor (28). This column (48) facilitates the transfer charge carriers between the source electrode (14) and semiconductor layer (28).The injection material is preferably an organic compound such as 3-hexylthiophene, polyarylamine, poly(3,4-ethylenedioxythiophene)-polystyrenesulphonic acid or polyaniline.