Side-by-side ZnS/Si composite nanowires have been prepared by tin-catalyst confined growth. Simultaneous thermal evaporation of ZnS and Si powders provides precursor vapors that condense on metallic Sn droplets, resulting in the nucleation and anisotropic growth of composite nanowires made of adjacent ZnS and Si domains (see Figure). The diameters of composite nanowires can reach as low as 15 nm.