A polyorganosiloxane containing the units (HR2Si-O1 / 2) HM units, (Si-O4 / 2) Q units, (R1Si-O3 / 2) T units and (R2Si-O2 / 2) D units in a ratio of from 2:1:0:0 to 6:4:2:2, or (HR2Si-O1 / 2) HM units, (R1Si-O3 / 2) T units, (R2Si-O2 / 2) D units and (R2(R1O)Si-O1 / 2) in a ratio HM:T:D:alkoxyM of from 1:2:0:0 to 3:4:2:2 is described, where R are identical or different, non-halogenated or halogenated hydrocarbon radicals having from 1 to 18 carbon atoms per radical, or are OR1, where R1 is a monovalent, unsubstituted or substituted hydrocarbon radical having from 1 to 8 carbon atoms, and in each molecule there are at least 3 Si-bonded hydrogen atoms. The polyorganosiloxanes are particularly useful as crosslinking agents in addition curable elastomer formulations.