We have investigated the switch-on transients of polycrystalline silicon thin film transistors. The investigation has been performed on devices fabricated on films with very long crystal domains obtained by excimer-laser annealing crystallization. The measurement of switch-on transient reveals that the device transient behavior depends significantly on both temperature and illumination. The temperature dependence, under dark and illumination, suggests that the mechanism accountable for the transient behavior of thin film transistors cannot be attributed only to carrier trapping but rather to a more complex mechanism involving carrier generation and recombination in the device body. (C) 2005 Elsevier B.V. All rights reserved.