Amorphous silica nanowires generally grow in either a metal-catalyzed vapour–liquid–solid (VLS) process or a solid–liquid–solid (SLS) process. So far, ordered alignment of impurity-free SiO_x (1 < x < 2) nanowires has not been achieved. In this study, without using metal catalysts, laterally aligned amorphous silica nanowire arrays have been successfully synthesized on a Si(100) substrate surface at ∼700–1100 °C. These amorphous silica nanowires have diameters of ∼100–350 nm and lengths of ∼1–20 μm, which are uniformly decorated with ∼4–11 nm SiO nanocrystals as a result of possible thermal decomposition of amorphous silica at high temperature. A carbon-assisted and lattice strain driven mechanism might be responsible for the lateral alignment of these SiO nanocrystal decorated amorphous silica nanowires.