Electrical properties in the subthreshold region are studied in two types of field effect transistors: laser crystallized-polysilicon thin film transistors (LC-TFTs) and solid phase crystallized-polysilicon thin film transistors (SPC-TFTs), For LC-TFT the active layer is crystallized by using one shot of a very large area excimer laser with a fluence of 600 mJ/ cm(2), whereas the active layer for SPC-TFT is crystallized by a thermal annealing at 600 degreesC in vacuum. LC polysilicon layer exhibits a higher degree of crystallinity than the SPC one. Electrical measurements on the TFTs are performed from room temperature to 120 degreesC. The analysis of the transfer characteristics shows that the subthreshold current is thermally activated with a different gate voltage dependence for each type of TFTs. The electrical behavior in the subthreshold region is correlated with the quality of the polysilicon active layer, For LC-TFT, conduction is mainly due to thermal emission of carriers over intergranular barrier energy, and it is convenient with a discrete distribution of defects in the active layer, mainly located at the grain boundaries. On the other hand, for SPC-TFTs, a mechanism of multiple-trapping and/or generation/recombination process of carriers from defects, rather uniformly distributed in the active layer, predominates in the electrical conduction. (C) 2002 Elsevier Science Ltd. All rights reserved.