Thin silicon films are of great importance for large-area electronic applications, for example, as the basis for switching electronics in flat-panel display devices or as the active layer of solar cells. In this paper, we show that silicon nanoparticles have the potential to be used as raw material for further processing toward a microcrystalline silicon film. This can be done by thermal treatment with a reduced thermal budget because the melting point of the nanoparticles is much lower with only 60% of the equilibrium melting temperature of silicon. Coagulation processes of liquid droplets then lead to the growth of microcrystalline silicon in agglomerated nanoparticles. We demonstrate by in situ transmission electron microscopy (TEM) and differential thermal analysis that silicon nanoparticles with a size of approximately 20nm start melting at around 1000K; furthermore, the TEM observations directly demonstrate the details of the coagulation process leading to microcrystalline silicon.