The epitaxial growth of 1D nanostructures is of particular interest for future nanoelectronic devices such as vertical field-effect transistors because it directly influences transistor densities and 3D logic or memory architectures. Silicon nanowires (SiNWs) are a particularly important 1D nanomaterial because they possess excellent electronic and optical properties. What is more, the scalable fabrication of vertically aligned SiNW arrays presents an opportunity for improved device applications if suitable properties can be achieved through controlling the alignment and density of SiNWs, yet this is something that has not been reported in the case of SiNWs synthesized from Au films. This work therefore explores the controllable synthesis of vertically aligned SiNWs through the introduction of an annealing process prior to growth via a Au-catalyzed vaporliquidsolid mechanism. The epitaxial growth of SiNWs was demonstrated to be achievable using SiCl4 as the Si precursor in chemical vapor deposition, whereas the alignment and density of the SiNWs could be controlled by manipulating the annealing time during the formation of Au nanoparticles (AuNPs) from Au films. During the annealing process, gold silicide was observed to form on the interface of the liquid-phase AuNPs, depending on the size of the AuNPs and the annealing time. This work therefore makes a valuable contribution to improving nanowire-based engineering by controlling its alignment and density as well as providing greater insight into the epitaxial growth of 1D nanostructures.