Due to the high attenuation in vitreous silica, acoustic attenuations in the THz regime are typically measured by incoherent techniques such as Raman, neutron, and X-ray scattering. Here, we utilized multiple-quantum-well structures to demonstrate acoustic spectroscopy of vitreous silica up to ∼740 THz. The acoustic properties of silica thin films prepared by physical and chemical deposition methods were characterized in the sub-THz regime. This technique can be useful in resolving debated issues relating to Boson peak around 1 THz.