Using a hot filament (≊1400 °C) to activate borazine (B3N3H6) molecules for subsequent reaction with a direct line-of-sight substrate, transparent boron nitride films as thick as 25 000 Å have been grown for substrate temperatures as low as 100 °C. The minimum temperature is determined by radiative heating from the adjacent hot filament. The low temperature BN films show no indication of crystallinity with x-ray diffraction (XRD), but the opaque BN deposit produced on the hot filament is identified by XRD as polycrystalline h-BN. X-ray photoelectron spectra (XPS) show the films to have a B:N ratio (within experimental error) of 1:1 with no other XPS detectable impurities above the 0.5% level. Both Raman and infrared (IR) spectroscopy are characteristic of h-BN with small amounts of hydrogen detected as N–H and B–H bands in the IR spectrum. The important feature of this method is the separation and localization of the thermal activation step at the hot filament from the surface reaction and film growth steps at the substrate surface. This allows both higher temperature thermal activation and lower temperature film growth.