 He remained at LMU as a Privatdozent until he was called to the University of Leipzig in 1926 as an extraordinarius professor of mathematical physics.In 1926, Wentzel, Hendrik Kramers, and Léon Brillouin independently developed what became known as the Wentzel–Kramers–Brillouin approximation, also known as the "WKB approximation", "classical approach", and "phase integral method".He became ordinarius professor in the Chair for Theoretical Physics, at the University of Zurich, when he succeeded Erwin Schrödinger, in 1928, the same year Wolfgang Pauli was appointed to the ETH Zurich.