Munster, twice champions and twice runners-up, will have to reproduce the dogged resistance that got them past Harlequins in London in the quarter-finals if they are to overcome French league pacemakers Clermont in Montpellier on Saturday 1600 GMT.
Toulon, last year's Amlin Cup runners-up, take on 2011 Premiership champions Saracens at Twickenham on Sunday at 1400 GMT with the fly-half showdown between Jonny Wilkinson and Owen Farrell the focal point of the afternoon.
The money pouring into Toulon has turned them into something of a pre-retirement home for some of the world's leading players and their multi-national mix has lifted the club to unprecedented heights.
Last season they were Top 14 runners-up having reached the Heineken Cup quarter-finals the previous year in their debut season while this time they are breathing down Clermont's neck domestically and on the cusp of the biggest final of all.
Saracens, who also reached the semis in 2008 when they were pipped by Munster, are clear leaders of the English Premiership so it is a meeting of teams right at the top of their game.
Progress to the final, and possible victory, would cap an extraordinary turnaround for Toulon, who were relegated to the second-tier in 2000 due to financial problems.
President Mourad Boudjellal has invested huge amounts to build a team that won promotion in 2008 and now ranks among the most powerful in the game.
"It's unthinkable - who would have thought a couple of years ago that Toulon would be playing at Twickenham?" Boudjellal said.
"Two years ago in the quarter-final against Perpignan we were not ready for it. Now, the squad and the city have matured.
"I may be one of the few Top 14 presidents to be born in his club's city. I'm from here, so it's special to see my town live this.
"The beautiful thing in that is that we're going to play in the greatest rugby venue with the English god of rugby, Jonny Wilkinson. We were dreaming of bringing him back there."
Wilkinson, 34 next month, is playing some of the best rugby of his career and it was his faultless kicking display that got Toulon past Leicester in the quarters.
Up against him is Farrell, the 21-year-old now filling his England number 10 shirt and regularly compared with the 2003 World Cup-winner.
"Jonny is someone I respect massively," Farrell said this week. "He set the standard and pushed the bar right up as far as fly-halves are concerned and he's still doing that today."
Despite the star-studded nature of Toulon's team, perhaps the more pragmatic Saracens approach does not seem to have struck a nerve with London neutrals as by Wednesday only around 20,000 tickets had been sold for the 80,000-capacity stadium.
There will be no empty seats in Montpelier, however, as the relentlessly consistent Clermont, the only semi-finalists to have won all seven of their tournament games this season, look to go one better than last year when they lost to eventual champions Leinster in Bordeaux.
That made it four titles in five years for Irish clubs and Munster, appearing in their 10th semi-final, are not about to let that influence disappear without a struggle.
The Province's rugby identity has been forged on remarkable Heineken Cup triumphs against the odds but captain Paul O'Connell, immense against Harlequins in the quarters, says Saturday could be the stiffest test of all.
"It's probably the biggest challenge in my time in Munster," said the lock. "I think their bench would start on most Six Nations teams not to mention Heineken Cup teams, so they have a phenomenally strong squad.
"You can win games sometimes with eight or nine players playing well, we're going to need 15 players playing out of their skins and then we're going to need everyone coming off the bench to make a big impact as well."