Abstract: The invention concerns a method for preparing hydrogenated alkylmonosilanes, by catalytic hydrogenolysis, under hydrogen pressure, of halogenoorganopolysilanes, improving known methods, in particular by facilitating implementation, and in terms of cost-effectiveness and performance which are shown by the efficiency of the resulting hydrogenated monosilanes. In said method the starting polysilanes are of the type: (CH3)Cl2Si—SiCl(CH3)2; (CH3)Cl2Si—SiCl2(CH3); (CH3)Cl2Si—Si(CH3)3; (CH3)2ClSi—SiCl(CH3)2; (CH3)Cl2Si—SiCl(Ch3)—SiCl2(CH3); (CH3)Cl2Si—Si(CH3)(SiCH3Cl2)—SiCl2CH3. The hydrogenated monosilanes CH3H2ClSi; (CH3)2HClSi; CH3HCl2Si are obtained by contacting said polysilanes with gaseous hydrogen under pressure, in the presence of a catalytic system AB comprising a hydrogenation catalyst precursor A and an auxiliary B for dissolving precursor A in the reaction medium. Said catalytic system is further characterized in that it is reductant-free.