De Jong, who is set to join Barcelona from Ajax ahead of the 2019-2020 season, was the Oranje's star man in Guimaraes.
England then fell apart in extra time, John Stones giving the ball away to Memphis Depay, which led to Kyle Walker's own goal, before Ross Barkley's lapse allowed Quincy Promes to strike a decisive blow.
Amid the carnage of mistakes from both sides, De Jong was a calming presence in midfield for Koeman's men with his 105 passes and 128 touches the most of anyone on the pitch.
While De Jong shone with his typically precise passing, he also made 13 recoveries and completed five tackles in a diligent defensive display that impressed Koeman.
"Of course he was player of the match, it was well deserved," Koeman said. "Most of the people are always looking at what he does with the ball, how calm he is, but in defence how many balls he is winning in midfield - it's fantastic to see Frenkie play like this.
"It looks so easy but it isn't, it was really well deserved tonight."
The final will see Netherlands centre-back Virgil van Dijk, who has been touted for the Ballon d'Or, test himself against Portugal superstar Cristiano Ronaldo – a five-time winner of the award.
But Koeman feels the clash between Van Dijk and Ronaldo should not be allowed to overshadow the showpiece in Porto.
"It isn't a battle between two players, it's Portugal and Holland," he added. "We know it's impossible sometimes to have good defending against Cristiano Ronaldo but we want to keep the ball, with good possession, as then he can do nothing in attack.
"We don't stop after tonight. There's always something to improve, but we are in a good way, the team is happy and confident in the way we like to play.
"We have big talents coming through, experience in the team, two players who won the Champions League, this experience to play and win a semi-final, then play the final on Sunday, it makes everything much easier."