The leakage current I-L of offset gate n- and p-channel excimer laser annealed polycrystalline silicon thin-film transistors (polysilicon TFTs) has been investigated experimentally. It has been found that the leakage current is almost independent of the polysilicon layer quality, in n-type polysilicon TFTs, I-L arises from band-to-band tunneling due to extension of the drain junction to the gate end by diffusion of phosphorus ions fr om the drain contact within the offset region. In p-channel TFTs, I-L first increases rapidly and then saturates at high drain voltages. This leakage current behavior is explained qualitatively by a model based on the change of the effective offset length, caused by the applied drain voltage on the positive ions of boron, diffused from the drain contact within the offset region.