Process for preparing trisilylamine and polysilazanes in the liquid phase, wherein (a) at least monochlorosilane dissolved in a solvent is placed in liquid form in a reactor, where the solvent is inert towards monochlorosilane, ammonia, TSA, DSA and polysilazanes and has a boiling point higher than that of TSA, and (b) the reaction is carried out in the reactor by introducing ammonia (NH 3) in a stoichiometric excess relative to monochlorosilane into the reactor and (c) the reactor is depressurized, a pressure of from 0.5 bar a to 0.8 bar a is set, the product mixture (TSA, L, NH 4 Cl, DSA, NH 3) is conveyed in gaseous form from the top of the reactor through a distillation unit, the NH 3 is separated off by means of a vacuum unit, the product mixture (TSA, L, NH 4 Cl, DSA) is condensed in a heat exchanger and the product mixture (TSA, L, NH 4 Cl, DSA) is collected in a vessel, (d) the product mixture is subsequently filtered by means of filter unit, with solid ammonium chloride (NH 4 Cl) being separated off from the product mixture, and the filtrate is conveyed from the filter unit into the distillation column in which DSA is separated off at the top from the mixture (TSA, L), and the mixture (TSA, L) is fed into a distillation column in which TSA is separated off at the top from the solvent, with the solvent being recovered, and (e) the bottom product mixture (PS, L, NH 4 Cl) is conveyed from the reactor through a filter unit in which solid ammonium chloride (NH 4 Cl) is separated off, to give a mixture of polysilazanes and solvent which is collected in a vessel 9, and (f) the mixture of polysilazanes and solvent is subsequently fed to a distillation column in which the major part of the solvent is recovered at the top and a concentrated mixture of polysilazanes and solvent is taken off from the bottom. (a) at least monochlorosilane dissolved in a solvent is placed in liquid form in a reactor, where the solvent is inert towards monochlorosilane, ammonia, TSA, DSA and polysilazanes and has a boiling point higher than that of TSA, and (b) the reaction is carried out in the reactor by introducing ammonia (NH 3) in a stoichiometric excess relative to monochlorosilane into the reactor and (c) the reactor is depressurized, a pressure of from 0.5 bar a to 0.8 bar a is set, the product mixture (TSA, L, NH 4 Cl, DSA, NH 3) is conveyed in gaseous form from the top of the reactor through a distillation unit, the NH 3 is separated off by means of a vacuum unit, the product mixture (TSA, L, NH 4 Cl, DSA) is condensed in a heat exchanger and the product mixture (TSA, L, NH 4 Cl, DSA) is collected in a vessel, (d) the product mixture is subsequently filtered by means of filter unit, with solid ammonium chloride (NH 4 Cl) being separated off from the product mixture, and the filtrate is conveyed from the filter unit into the distillation column in which DSA is separated off at the top from the mixture (TSA, L), and the mixture (TSA, L) is fed into a distillation column in which TSA is separated off at the top from the solvent, with the solvent being recovered, and (e) the bottom product mixture (PS, L, NH 4 Cl) is conveyed from the reactor through a filter unit in which solid ammonium chloride (NH 4 Cl) is separated off, to give a mixture of polysilazanes and solvent which is collected in a vessel 9, and (f) the mixture of polysilazanes and solvent is subsequently fed to a distillation column in which the major part of the solvent is recovered at the top and a concentrated mixture of polysilazanes and solvent is taken off from the bottom.