Siegmund III Christoph Graf von Schrattenbach, also Sigismundus (28 February 1698 – 16 December 1771) was Prince-Archbishop of Salzburg from 1753 to 1771.

After studying theology in Rome, Schrattenbach was ordained a priest in 1723 and obtained a seat in the Salzburg cathedral chapter in 1733.

During his tenure Leopold Mozart as well as his son Wolfgang Amadeus were appointed members of the episcopal court orchestra and he financed the grand tour across Europe.

Between 1764 and 1767, Sigismund was responsible for the construction of the Sigmundstor, a road tunnel that connects the Salzburg Altstadt with the Riedenburg quarter through the Mönchsberg mountain.

His funeral service on 2 January 1772 was the occasion for the first performance of Michael Haydn's Requiem Missa pro defuncto Archiepiscopo Sigismondo[2] written in his honour.