Transient photoconductivity measurements were carried out in thin-film transistors of silicon-on-insulator structures which were formed by oxygen implantation and subsequent lamp annealing. They show that traps arising primarily due to surface states at the top silicon–oxide interface are responsible for the observed dispersive transport in these films. As the gate voltage is increased and more holes are pulled to the surface, the form of transients changes from dispersive to non-dispersive due to saturation of the surface traps. Upon further increase of the gate voltage the form and the magnitude of the photocurrent prior to recombination remains unchanged, but the observed decay time gets longer for higher gate voltages. This occurs due to a reduction in the recombination centre density for the majority carriers corresponding to the movement of the demarcation level.