The Ospreys beat reigning champions Munster 45-10 at the Liberty Stadium on Friday night to book their ticket into their second final in three seasons. They were champions in 2010, beating Leinster at the RDS, and semi-finalists last season.
The two teams will be eligible for up to 50% of the tickets in each category and details of sales will be issued by both sides as soon as possible.
Leinster out-half Jonathan Sexton was named as the RaboDirect PRO12 man-of-the-match against Glasgow after scoring 14 points.
But Ospreys number 10 Dan Biggar toped that with a 25-point haul against Munster to pass 300 points for the season and 1000 in his career at the Ospreys.
"The Ospreys were pretty outstanding against Munster and it's going to be a difficult game," admitted Sexton. "They beat us in Dublin two years ago in the final, and they beat us at the RDS this season as well."
Williams has already won three league titles and two Grand Slams and was named the IRB World Player of the Year in 2008.
He scored a record 58 tries in 87 Tests for Wales and also scored two tries for the British & Irish Lions in four Tests during two tours. He was the RBS 6 Nations Player of the Tournament in 2008.
"It has been great been involved in some small way with Shane's career and it would be wonderful to send him into retirement with another title," said Biggar.
"But we know that Leinster are the best team in European rugby and the RDS is one of the toughest places to go and play.
"It was great to play so well in beating Munster, but you don't win anything in a semi-final. We are under no illusions as to how hard it is going to be in Dublin and how well we are going to have to play."
Leinster will be hoping it will be third time lucky in the final having been beaten 17-12 by the Ospreys in 2010 and going down 19-9 to Munster at Thomond Park last year.