In the German Democratic Republic, he served as the longtime head of the powerful Agriculture Department of the SED Central Committee.
[1] From 1972 to 1973, he attended the "Karl Marx" Party Academy and then was sector head in the Central Committee of the SED from 1974 to 1981.
[1] From 1981 to 1982, he was the First Secretary of the SED district leadership for central organs of agriculture and the food industry, succeeding Fritz Klopprogge.
[1] In 1974, Semmelmann was awarded the Patriotic Order of Merit in bronze, in 1984 in Gold and the Banner of Labor.
At its last session on 3 December 1989, the Central Committee elected Semmelmann to a commission tasked with analyzing the causes of the crisis in the SED and in society.