Silicon waveguide structures are a viable alternative for the transmission of signals over a wide range of frequencies, and new fabrication methods are key to increased applications. In this work, THz transparency of silicon-core, silica clad fibers, refined using a traveling solvent method, is demonstrated. The ≈ 200 µm core of these fibers is shown to have good transmission from 4.8–9 µm and 1–7 THz. Fibers were drawn on a conventional optical fiber tower using the scalable molten core technique and CO_2 laser annealed, resulting in large-grain crystalline cores with broadband transmission. The spectral properties are comparable to those of rectangular guides of similar cross-sectional area cut from high resistivity float zone silicon wafers.