In 1960 Chern moved to the University of California, Berkeley. He worked and stayed there until he became an emeritus professor in 1979. In 1961, Chern became a naturalized citizen of the United States. In the same year, he was elected member of the United States National Academy of Sciences. "My election to the US National Academy of Sciences was a prime factor for my US citizenship. In" 1960 "I was tipped about the possibility of an academy membership. Realizing that a citizenship was necessary, I applied for it. The process was slowed because of my association to Oppenheimer. As a consequence I became a US citizen about a month before my election to academy membership."In 1964, Chern was a vice-president of American Mathematical Society (AMS).