Crystallization behavior of amorphous silicon (a-Si) using the field aided lateral crystallization (FALC) process was investigated. The lateral crystallization of a-Si was remarkably enhanced at the negative electrode side with the aid of an electric field, while it was retarded at the positive electrode side. FALC velocity using Ni was as high as 11 mum/h at 500 degreesC with an electric field of 4 V/cm. In addition, the nickel silicide phase, known to be a mediator for low temperature crystallization, can be driven from either the drain to source or source to drain in the active layer, depending on the bias conditions during crystallization. Thus, the defects originating from residual nickel silicide can be driven out from the channel region. Due to such an asymmetric location of the residual nickel silicide, the leakage current of the polycrystalline silicon thin film transistor (poly-Si TFT) using the FALC process showed a leakage current of approximately one order of magnitude lower when we reversed the probing polarity. Therefore. it was judged that the judicious selection of the bias condition during the FALC process can be useful in improving the electrical properties of poly-Si TFT.