He was shot in prison by the Nazi occupiers in 1942, and is buried at the Père Lachaise Cemetery in Paris.

Lenin made concessions to his interlocutors, so that back in France, Semard justified the CGTU's membership in the SRI.

During his imprisonment, he wrote numerous articles in La Vie Ouvrière where he pleaded in particular for open mass unionism that did not assert any doctrine.

After the Molotov–Ribbentrop Pact he was dismissed from his role as the Councillor of the Seine Department and returned to work as a railway worker and was later imprisoned on accounts of embezzlement.

In the beginning of 1942, Pierre Semard was transferred from Bourges to the Gaillon internment camp where he found himself with common law prisoners.