Thin-film transistors (TFTs), fabricated on solid-phase-crystallized polycrystalline silicon (polysilicon) films subjected to laser annealing, were studied. For the resulting large-grain polysilicon TFTs, a model is proposed that takes into account two well-distinguished regions within the channel of the transistor: the intra-grain region and the grain boundaries. By using this model, we found that the extracted on-voltage is mainly grain-boundary dependent while the maximum transconductance is mostly intra-grain defect dependent. Moreover, with the aid of this model, the physics of the large-grain polysilicon TFTs becomes more evident and an optimal laser energy density was found for best device performance.