The referee for the last two Heineken Cup finals, which were won by Leinster in 2009 and Munster in 2008, he was also in charge of Leinster's recent Heineken Cup semi-final defeat in Toulouse and Munster's quarter-final triumph at home over Northampton Saints.
Irishman Clancy will take charge of the first semi-final between the Ospreys and Glasgow Warriors at the Liberty Stadium, Swansea, on Friday night (K-O 7.05pm), while Welshman Owens will officiate in the game at the RDS between Leinster and Munster on Saturday (K-O 8.00pm).
Clancy made his Magners League debut in 2004, when he controlled the game between Borders and Newport Gwent Dragons. He has since gone on to referee in 35 Magners League matches.
One of the world's top 19 Test officials, Clancy made his representative debut in June 2008 taking charge of South Africa v Italy.