A fabricating method of a polycrystalline silicon thin film transistor includes forming a polycrystalline silicon layer on a substrate having first and second regions through a crystallization process using nickel silicide (NiSi_x) as a catalyst, patterning the polycrystalline silicon layer to form an active layer at the first region, leaving a nickel silicide residue at the second region, etching the nickel silicide residue with a solution including hydrofluoric acid (HF) and hydrogen peroxide (H₂O₂), forming a gate electrode over the active layer and forming a source and drain in the active layer.