Horst Paul Silvester Fischer (31 December 1912 – 8 July 1966) was a German doctor and member of the SS, executed in East Germany for crimes committed at Auschwitz-Birkenau concentration camp during World War II.
Fischer was born and orphaned and grew up with relatives in Dresden and Berlin. After attending medical school at the University of Berlin, Fischer received his medical degree in 1937. He had joined the SS in 1933, at the age of 20, and the Nazi Party four years later. He was transferred to Auschwitz-Birkenau in November 1942, where he became one of the highest-ranking physicians and participated at selections at the ramp from arriving trains. From November 1943 to September 1944 he was the main camp doctor in the infirmary of the Monowitz concentration camp. After the war he practised medicine in the German Democratic Republic for 20 years before trials of war criminals brought his identity into the light. He was tried by the GDR Supreme Court, found guilty and sentenced to death. After the Chairman of the State Council Walter Ulbricht refused clemency, Fischer was executed by guillotine (called Fallschwertmaschine in the GDR) in Leipzig on 8 July 1966.