This paper reports the studies of amorphous silicon (a-Si) thickness on the formation of aligned silicon nanostructures (ASiNSs) produced by aluminum-induced crystallization (AIC) of plasma-enhanced chemical vapor deposited a-Si. By varying a-Si thickness, the authors not only show that the thickness of an a-Si film has a significant impact on the formation of the ASiNS but also demonstrate that self-assembly is one of mechanisms that control the growth of such ASiNSs. This paper, for the first time, demonstrates that one can use AIC of a-Si to grow very straight-shaped ASiNS.