The kinetics of the low-pressure chemical vapour deposition of molybdenum on silicon from molybdenum hexafluoride and hydrogen are studied at 600 K and 8-315 Pa using a continuous how perfectly mixed reactor, equipped with a microbalance for in situ rate measurements. A significant contribution of reaction of the hexafluoride with silicon, which diffuses through the growing metal layer, to the overall rate obscures the kinetics of the reduction of molybdenum hexafluoride with hydrogen. A model is developed to obtain the intrinsic rates of the latter process. A ten-step elementary surface network is able to describe these rate data. According to this mechanism molybdenum hexafluoride adsorbs on the growing metal surface, leading to adsorbed fluorine atoms and solid molybdenum. The fluorine adatoms are removed from the surface by reaction with adsorbed hydrogen atoms. Trench fill experiments and their modelling furnish additional arguments for the proposed kinetic scheme.