Abstract: Controllable synthesis of one-dimensional nanowires (NWs) is crucial for their large-scale applications, but it usually requires complicated catalyst designs with multiple compositions and careful tuning of synthesis parameters. In this study, we performed a systematic investigation into the impact of the shape of Au particles on the geometry and composition of the obtained NWs. We discovered that octahedral, dodecahedral, and cubic Au particles selectively catalyze the growth of Ga, GaAs, and Ga/GaAs heterojunction NWs, respectively. The mechanism stems from the difference in the solubility of Ga in Au catalysts with distinct shapes (i.e., curvatures) due to the Gibbs–Thomson (G–T) effect: Au octahedrons (7.42 nm), featuring smaller curvature radii, enhance the solubility of Ga precursors, enabling efficient diffusion and faster growth of Ga NWs; Au dodecahedrons (11.22 nm) with larger curvature radii exhibit moderate Ga solubility, favoring the growth of GaAs NWs; Au cubes (10.51 nm) with intermediate Ga solubility, yield Ga/GaAs heterojunction NWs. Finally, we fabricated NW field effect transistors (FETs) and revealed that the Ga NWs exhibited promising electrical characteristics with a resistivity of 2.54 × 10⁻⁴ Ω·m, and GaAs NWs showed p-type characteristics. All these results illustrate the promising potential for tuning the geometry and composition of NWs by a single parameter, i.e., merely changing the shape of a single Au particle.