Amorphous silicon nanowires (a-SiNW) with an average diameter of ca. 20 nm were synthesized at about 950 degrees C under an Ar/H-2 atmosphere on a large area of a (111) Si substrate without supplying any gaseous or liquid Si sources. The Si substrate, deposited with a layer of Ni (ca. 40 nm thick), served itself as a silicon source for the growth of the a-SiNWs. In contrast to the well-known vapor-liquid-solid (VLS) for conventional whisker growth, it was found that growth of the a-SiNWs was controlled by a solid-liquid-solid (SLS) mechanism, which is analogous to the VLS model.