Hess took a leave of absence in 1921 and travelled to the United States, working at the United States Radium Corporation, in New Jersey, and as Consulting Physicist for the US Bureau of Mines, in Washington DC. In 1923, he returned to the University of Graz, and was appointed the Ordinary Professor of Experimental Physics in 1925. The University of Innsbruck appointed him Professor, and Director Institute of Radiology, in 1931.