Friday night (20 May) at the RDS Arena in Dublin sees Leinster welcome their provincial rivals Ulster and all 19,100 seats - including 700 additional ones installed over the weekend - sold out by Monday morning.
The Sportsground in Galway is also a sell-out for Connacht's rematch with defending champions Glasgow Warriors on Saturday (21 May) - the two faced off in the last round of the regular season.
And when you consider that there have already been record sales for the Guinness PRO12 Final at BT Murrayfield (28 May), the excitement is certainly building.
The two finalists will be confirmed this weekend but there is still time for fans to book their passage to Edinburgh.
And for Martin Anayi, managing director at PRO12 Rugby, the play-off semi-finals are the first chapter of a thrilling final fortnight for the league.
"This is fantastic news for both Leinster and Connacht," he said.
"I am sure there will be a fantastic atmosphere at both the RDS on Friday and the Sportsground on Saturday, we are anticipating two fantastic semi-finals.
"Ticket sales are also going very well for the Guinness PRO12 Final on 28 May and we are all anticipating a fantastic end to one of the most exciting seasons in PRO12 Rugby history.
"Fans from all over the league are descending on Edinburgh - now it is up to the four semi-finalists to try and book their place this weekend."
To be part of a great weekend in Edinburgh, and to buy tickets, hospitality or for accommodation information for the Guinness PRO12 Final, 28 May at BT Murrayfield visit: www.pro12rugby.com
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