This article demonstrates that metal-induced crystallization of PECVD grown amorphous silicon can be enhanced by the application of an external electrical field. Results from the observation of the Si(111) XRD peak height of the thermally annealed Si/Al/glass structure show that at very high vertical electric field (up to 7000 V/cm) no enhancement on aluminum induced crystallization of a-Si is found, whereas a clear enhancement of crystallization can be observed for the horizontal electric field as low as 100 V/cm. Mechanisms are proposed to explain such an observation, and it is suggested that the vertical Al/Si interdifussion process is prolonged under horizontal electric fields because of the presence of electron-collision caused by Al or AlSix ions, which allows more nucleation to take place.