In 1935, he corresponded with Abraham Fraenkel in Jerusalem and was implicated by the Nazi teachers' union as one who "keeps contacts to the Chosen People."

In 1935 and 1936, Hermann Weyl, head of the Göttingen mathematics department in 1933 until his resignation under Nazi pressure, made strong efforts to bring him to the Institute for Advanced Study in Princeton.

He, along with the rest of the staff of the German University in Prague, were detained in a Soviet prison camp, where he died of starvation on 4 August 1945.

[5][6] Gentzen's main work was on the foundations of mathematics, in proof theory, specifically natural deduction and the sequent calculus.

One of Gentzen's papers had a second publication in the ideological Deutsche Mathematik that was founded by Ludwig Bieberbach who promoted "Aryan" mathematics.