William Young and Gareth Gates are the finalists
The two contestants left to battle it out in next week's final are Gareth Gates and William Young - with Gareth favourite.
A total of 5.8 million people voted on Saturday in the ITV show.
Edinburgh University student Darius's performance of the Toploader hit, Dancing in the Moonlight, and Walker Brothers classic Make it easy on Yourself won 20.9% of the vote.
But the 21-year-old told viewers: "This is not the end. This is just the beginning."
Viewers were split between Gareth and Will as the contestants secured 39.8% and 39.3% respectively of Saturday's vote.
Viewing figures have grown steadily since the thousands of contestants were whittled down to 10 - who were then put to the public vote.
Poll favourites
Ahead of Saturday's show two polls put Gareth, 17, famed for his efforts to conquer his stammer, as the public's favourite.
He got 55% in a Sun newspaper telephone poll, compared with 27.5% for Darius and 17.5% for Will.
The results of a GMTV poll were closer, with 46% voting for Gareth, 27% for Darius and 25% for Will.
In Saturday's show, the four judges, Neil Fox, Nicki Chapman, Simon Cowell and Pete Waterman, picked two songs for each contestant to sing.
Darius was not expected to get as far as the semi-final after earning the tag of being arrogant and getting voted off a previous talent show, Popstars.
But a groundswell of support built for the student, with even Conservative leader Iain Duncan Smith getting behind him.
The Conservative leader was urged to declare his support for him at a press conference on Friday, in which he was invited to pose with a Darius T-shirt.
"Do you think this would be good for Darius?," he joked.
"I would be very happy if he was to win. I wish him the best of luck. I am not a great judge on these matters," he said.
However all four of the judges had predicted that Darius would be the next to leave while they forecasted a great future for him.
The final two now must carry out a week-long campaign to win the public's vote.
They will have to produce their own "manifesto" on why they should be chosen as Pop Idol and win the coveted recording contract.
The final is on 9 February.