Novel doughnut-like loop structures of silicon oxynitride were grown over a Si substrate via self-assembly of ordered nanowires. These hierarchical structures were formed by metallic gallium-catalyzed vapor-liquid-solid growth at high temperature under a flow of NH3 gas. The product was characterized by XRD, SEM, EDS mapping and XPS techniques. XRD characterization confirms the formation of Si3N4 and silicon oxynitride phases. The silicon oxynitride loop structures assembled by ordered nanowires have outer diameters of 10-14 mm and wall thickness of 2-3 mm. The nanowire bundles in a single loop exhibit a petal-like growth mode. EDS mapping verifies the elemental distribution over the structure. XPS analyses disclose the binding contribution from Si3N4, silicon oxynitride and silicon oxide. The formation mechanism of the self-assembled structures was analyzed based on the growth process.