The direct synthesis of methylchlorosilanes to react metallic silicon with methyl chloride in the presence of a copper catalyst yields a high-boiling fraction of methyl-chlorodisilanes as by-products. The invention provides a method for preparing monosilanes from the high-boiling fraction by reacting it with hydrogen chloride in the presence of an amine or amide catalyst. The reaction is effected under the condition that the amount of iron, aluminum, zinc, tin and compounds thereof present in the reaction system is less than the equimolar amount with the catalyst. This increases the conversion of disilanes into monosilanes.