During the war years, 1940 to 1945, Welker worked at Luftfunkforschungs Institut in Oberpfaffenhofen, but still maintained association (1942 to 1944) with the physicochemical institute of Klaus Clusius at the University of Munich.
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At the same time as the American researchers and independently, the German researchers Mataré and Heinrich Welker developed the first operational "French transistor" at Compagnie des Freins & Signaux Westinghouse in Aulnay-sous-Bois near Paris during the years 1945 to 1948.
In August 1948 German physicists Herbert F. Mataré (1912–2011) and Heinrich Welker (1912–1981), working at Compagnie des Freins et Signaux Westinghouse in Aulnay-sous-Bois, France applied for a patent on an amplifier based on the minority carrier injection process which they called the "transistron".