In this study, polycrystalline silicon fin-like thin-film transistors (poly-Si FinTFTs) with a wide drain structure are fabricated. The off leakage current of poly-Si FinTFTs with various extended wide drain lengths (LEX) is investigated. As LEX increases, the longitudinal electric field at the intrinsic drift/N+ drain junction decreases and improves the off leakage current derived from longitudinal band-to-band tunneling (L-BTBT). The off leakage current of poly-Si FinTFTs at different temperatures is also analyzed to investigate the leakage mechanisms. For poly-Si FinTFTs with a small LEX (= 0 and 0.8 mm), the weak dependence of leakage current on temperature indicates that the band-to-band tunneling (BTBT) is dominant. For poly-Si FinTFTs with a large LEX of 1.6 mm, the strong dependence of leakage current on temperature and the weak dependence of leakage current on drain voltage indicate that trap-assisted tunneling (TAT) is the dominant leakage mechanism. These results indicate that it is gate-induced drain leakage (GIDL), resulting from L-BTBT, that is effectively suppressed by increasing LEX.