Ronaldo's second-half header and a strike by his former Manchester United teammate Nani secured a 2-0 win against Wales in Lyon.
Portugal, which last reached the final of the competition in 2004, will face either host nation France or world champion Germany in Paris on Sunday.
This contest had been billed as clash between two of the world's top players -- Ronaldo and his Real Madrid teammate Gareth Bale.
But Bale, who has enjoyed a stellar tournament for a country which had never before qualified for the tournament, failed to match the exploits of his rival.
Ronaldo, who equaled Michel Platini's record of scoring nine career goals at the Euros, will now hope to exorcise the ghosts of 2004 when Portugal was beaten by Greece in a final held in its own backyard.
"I hope that [after the final] we'll be smiling and that it will be tears of joy in the end," Ronaldo told the tournament's official website.
"I've always said my dream was to win a trophy with Portugal. We're closer to doing it and I believe that we'll win.
"With a lot of work, humility and the spirit of self-sacrifice, which I have always shown in my career, these sorts of things are doable."
For Portugal, the road to the final has been long and arduous, often due to the team's own inadequacies.
While Wales enjoyed a rather enchanting run to its first major semifinal, Portugal's journey to its fifth could scarcely have been more different.
No other team had arrived at the last-four stage of the European Championship finals without winning a game in 90 minutes -- but Portugal, which drew all three of its group matches and only qualified in third place, has always managed to do just enough.
A last-16 win over Croatia, secured with just three minutes of extra-time remaining, was then followed by a penalty shootout triumph over Poland after the game had finished 1-1.
For all the exciting talent, and there is plenty even if this may not be a vintage Portuguese team, rarely has it looked impressive.
And yet, what it has done, is use its experience, its know-how and a resolute determination to ensure it will not be beaten.
In Renato Sanches, an 18-year-old midfielder recently bought by Bayern Munich for $36 million, Portugal has a player who will surely go on to take on Ronaldo's mantle.
But even the youngest and most precocious need guidance.
That guidance has come from Ronaldo, who despite failing to find his best form, has carried this team for long periods of the tournament.
His two goals in the 3-3 draw with Hungary, a game in which it trailed on three separate occasions, enabled Portugal to qualify as the third of the four best third-placed teams.
"It's what we have dreamed of since the beginning," Ronaldo added.
"We knew it would be a long road and we're still in the tournament. We have believed right from the start.
"We had difficult moments, but it's like I always say: it's better to start poorly and have a positive ending.
"We haven't won anything yet as I said a few days ago, but the dream is still alive."
For so long Ronaldo has been the one who has been responsible for pushing his team forward, but even he has appeared to be struggling both on and off the field of play.
First there was his outburst after his side's group draw against Iceland
, when he accused the island team of having a "small mentality" and claiming it would never achieve anything in the tournament -- a prediction which proved rather wide of the mark.
Then there was his penalty miss in the goalless draw with Austria
which was followed a few days later by his decision to throw a reporter's microphone into a lake
while out on a prematch walk.
But for all his histrionics and his ability to split public opinion, few can doubt his talents and the records he has broken.
His 61 goals in 132 games makes him Portugal's top scorer, while he is the only player to have scored in four consecutive European Championship finals.
But his struggles in France have been well documented -- his wayward shooting, the lack of usual poise on front of goal and his waning influence on games has become more noticeable.
It is in sharp contrast to his Real Madrid teammate Bale, who was responsible for creating one of the only real opportunities of a tight and cagey first period.
Bale, who scored in each of Wales' first three group games, picked the ball up in his own half and drove through the Portuguese midfield before unleashing a fierce effort straight at goalkeeper Rui Patricio.
While the first half may have been rather uninspiring, the second was anything but as Ronaldo and Portugal took control of the contest.
Just five minutes of the second half had passed when Ronaldo rose highest at the far post to meet Raphael Guerreiro's cross and power a header into the top corner.
Wales, still dazed from conceding the opening goal, was then dealt another blow just three minutes later.
Once again it was Ronaldo at the heart of the move, flashing a driven effort into the penalty area -- and Nani, who on Tuesday joined Valencia, diverted the ball past stranded goalkeeper Wayne Hennessey.
Wales, pushing forward in search of a way back into the contest, began to leave holes at the back and was fortunate not to fall further behind.
First, Hennessey failed to hold Nani's shot and Joao Mario somehow contrived to fire the rebound wide of the post with the goal gaping.
Moments later it was Danilo who came close, his short squirming under Hennessey's body before the goalkeeper recovered to stop the ball on the line.
Wales huffed and puffed, with Bale unleashing a couple of efforts from long range as Portugal sat back and hit its opponent on the counter attack.
Roared on by thousands of fans, Wales continued to move forward but it lacked the precision and quality which had been so evident during its run to the final four.
In the immediate aftermath of this defeat, it is easy to to forget that when Chris Coleman took over this team four years ago that it sat 117th in the world rankings and had not qualified for a major tournament since 1958.
Just to play in these finals was an achievement -- but what this team has done over the past month will change the landscape of football in Wales forever.
Not only did it qualify ahead of England and outlast it, it played with a sense of pride, passion and least of all, quality.
Some had labeled Wales a "one-man team" with Bale cast as the superstar dragging 10 other players along with him.
Yet, such an assertion was to prove folly.
Wales have been a joy to watch throughout the tournament. Like Iceland, it boasts a connection between the team and supporters which few others can match, bar the Irish of course.
It has inspired, it has brought hope and it has revitalized football in the country -- but this was a fairy tale without the ending so many had yearned for.
For Ronaldo, though, the end is not yet written.