Thin films of polycrystalline silicon are of great importance for large-area electronic applications, providing, for example, the switching electronics in many flat-panel displays. Polycrystalline silicon is typically produced by annealing films of amorphous silicon(1) that have been deposited from the vapour phase, and much research is focused on lowering the crystallization temperature. It is known that the solid-phase crystallization temperature of amorphous silicon can be reduced by the addition of certain metals(2), such as nickel(3). Here we show that the rate at which this metal-induced crystallization takes place is markedly enhanced in the presence of an electric field. For example, the crystallization time at 500 degrees C decreases from 25 hours to 10 minutes on application of a modest (80 V cm(-1)) electric field. No residual amorphous phase can be detected in the films. A thin-film transistor fabricated from such a film exhibits a field-effect mobility of 58 cm(2)V(-1)s(-1), thereby demonstrating the practical utility of these materials.