The key feature of the source-gated transistor is the source barrier. Here we report the analysis of source-gated transistors in amorphous silicon having Schottky source barriers. It is shown that the changes in current are well described by thermionic-field emission of electrons through the reverse biased barrier and the effect of the electric field induced by the gate. For high barriers and low currents the change of effective barrier height with gate voltage is in good agreement with that obtained from activation energy measurements but at high currents and low barriers there is evidence that the current is being limited by other factors apart from thermionic-field emission from the source. (c) 2006 Elsevier Ltd. All rights reserved.