Only once have they overcome the last-four hurdle and then they were beaten in the final by Greece as hosts at Euro 2004.
If you include their defeat in the semi-finals of the 2006 World Cup and a loss at the Euros in 1984, they are becoming all too familiar with the pitfalls of this stage of major tournaments.
Portugal's conquerors in their recent last-four clashes have included football powerhouses France, at Euro 2000 and the World Cup in 2006, and Spain at Euro 2012.
Should they lose to Wales, playing their first major tournament in 58 years and their first ever semi-final, it would be a devastating blow.
Yet Wales are arguably the form team coming into the match.
Chris Coleman's side have revelled in their underdog status to win their group, which also included England, Russia and Slovakia, ease out British rivals Northern Ireland in the last 16 and sweep past heavy favourites Belgium in the quarters.
Portugal are yet to win a match at the tournament inside 90 minutes, having drawn all three group games, beaten Croatia in extra time and squeezed past Poland on penalties.
Things are yet to click for Portugal, and by extension for captain Cristiano Ronaldo, who has at times looked exasperated by his team mates' attacking shortcomings.
Yet Portugal are unbeaten in 12 competitive internationals since Fernando Santos took over as coach at the start of the Euro 2016 qualifying campaign.
With Ronaldo's Real Madrid team mate Pepe marshalling an increasingly assured defence, they will be tough to break down.
Especially for a Wales side deprived of one of their most talented creative influences in midfielder Aaron Ramsey, who will be suspended after picking up a booking in the win over Belgium.
While Gareth Bale has been Wales's attacking talisman, scoring three times to lift them out of their group, Ramsey has been arguably their most influential player, scoring one and producing four assists in the run to the last four.
The match is likely to be billed as a contest between the two most expensive players in the world -- Ronaldo, who will play a record third European Championship semi-final, and his Real Madrid team mate Bale.
Perhaps ominously for Wales, Ronaldo has netted twice in each of his last two games in Lyon for club and country.
(Editing by Ed Osmond)
