European Rugby Cup confirmed that the last-four clash will be played in Dublin on 28 April if the province win - if they lose to Saracens, it will take place at Twickenham.
Ulster's opponents will be Toulon or Leicester.
The first semi-final, on 27 April, will be staged at Stade de la Mosson in Montpellier, with the winner of Clermont Auvergne v Montpellier hosting Harlequins or Munster.
Mark Anscombe's side will take renewed confidence into Saturday's game after securing an historic 22-18 away win over Leinster in the PRO12 - their first since 1999.
Ulster, who coincidentally last won the Heineken Cup in 1999, were runners up to Leinster last season after losing 42-14 in London.