The analysis of the overshoot transient currents in polysilicon TFTs was found to provide valuable information oil the nature of band gap states. However, there is no systematic study of the undershoot effect which occurs when the device gate is switched from strong to weak or moderate inversion. The aim of the present work is to present an analysis of the undershoot effect in the temperature range of 100 - 400 K. The results suggest the trapping and emission of electrons in the band gap states as the responsible mechanism. Both trapping and emission processes were found to obey the stretched exponential law, while thermally activated time constants, with material related activation energies, were obtained. (c) 2007 Elsevier Ltd. All rights reserved.