Thin polycrystalline silicon (poly-Si) films on glass are of great interest for electronic and photovoltaic applications. In this paper we report the successful realisation of thick (5 microns), large-grained (5 microns), continuous and smooth poly-Si films on glass at a temperature below 700°C. This significant technological milestone was achieved by using ion-assisted deposition (IAD) of silicon at 630°C for thickening a thin poly-Si seeding layer made on the glass at about 500°C by aluminium-induced crystallisation of amorphous silicon. Transmission electron micro-graphs reveal an epitaxial relation between about 50% of the grains of the IAD-grown layer and the seeding layer, while the remainder grew with a different orientation than the seed grains. The grain size of the IAD-grown poly-Si film is determined by the grain size of the underlying polySi seeding layer, a clear experimental proof of the “seeding layer concept”.