The invention relates to a process for preparing trisilylamine and polysilazanes in the liquid phase, in which ammonia is introduced in a superstoichiometric amount relative to 5 monochlorosilane which is present in an inert solvent. Here, a reaction in which trisilylamine and polysilazanes are formed proceeds. TSA is subsequently separated off in gaseous form from the product mixture. The TSA obtained is purified by filtration and distillation and obtained in high or very high purity. The bottom product mixture is conveyed from the reactor through a filter unit in which solid ammonium chloride is separated off to give a liquid mixture of polysilazanes and solvent. This is fed to a further distillation to recover solvent. As a result of the NH3 being introduced in a superstoichiometric amount relative to monochlorosilane, monochlorosilane is completely reacted in the reactor. This completely prevents the reaction of monochlorosilane with additional disilylamine formed in small amounts to form solid ammonium chloride in the downstream plant parts for purification of the TSA. The solutions filtered downstream of the reactor are accordingly completely free of solids.