The Portuguese forward became the first player to score in six straight 'Clasicos' away from home, opening his account from the penalty spot before hitting a rebound just before the hour mark as Real Madrid strolled to a 4-2 aggregate victory.
Real are through to the Cup final for a record 38th time - having won 18 of their previous finals.
Afterwards the Ballon d'Or runner-up hailed the attitude of his teammates in their sweeping victory.
"From the first minute to the last we were very focused, with a great attitude," he said.
"We played better than Barca, scoring three goals in the Nou Camp is extremely difficult.
"Lately whenever we play here we do very well. We play better here than at home.
"We must continue with this confidence. Most of the players like to play here and things are going well for us."
Ronaldo opened the scoring when he picked himself up after being felled by Gerard Pique in the 13th minute, drilling a powerful low penalty into the corner past Jose Manuel Pinto.
Barca dominated possession but rarely threatened and Ronaldo doubled the lead when he collected a rebound from a 57th-minute Angel Di Maria effort and stroked the ball into the net with Pinto stranded.
It was his 12th goal in 18 appearances against barcelona since joining Real in 2009 - and his second double in as many games at a stunned Nou Camp.
Real rubbed salt in the wounds of their arch-rivals when Raphael Varane, who netted the equaliser in the 1-1 draw in last month's first leg at the Bernabeu, rose above the defence at a 68th-minute corner and sent a header arrowing into the net off the crossbar.
Jordi Alba pulled one back in the 89th minute but it was far too late for Barca who conceded three goals to Real at home for the first time since a 3-3 draw in March 2007.
They had not lost to the Madrid club by two goals at their giant arena in more than a decade.
"We are coming away with the feeling that we have done a very good job," Real captain Sergio Ramos said afterwards
"You always suffer against Barcelona because they look for the spaces and they make things hard for you but we fought very well," the Spain international added.
"I have always said that he (Ronaldo) is the best in the world and he always does the business in these games."
Jordi Roura, Barcelona's acting coach, is confident his side will soon emerge from their dip in form.
"We must quickly forget this and focus on the very important titles we have to play for," he told Marca
"Madrid were terribly effective against us. I do not think they were so superior, the differences were small details.
"We had dreams of being in another final and obviously it is a disappointment, but the message has to be optimistic.
"There is no need to reproach the team. We must have absolute confidence this team can depart from this rut.
"We have lost the cup but in the league, we are strong favourites. And we have the return match with Milan and will try to come through the tie.
"We have significant challenges in two special competitions and will fight to the end."
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