Spurs have come through four matches to reach the last four of the competition, which will be staged at Wembley Stadium where Spurs have played their home fixtures this season.
However, Dier has claimed that the atmosphere will be different for the North Londoners due to the equal number of both Spurs and Manchester United supporters.
The 24-year-old is quoted by the Daily Mail as saying: "The FA Cup is a completely different competition, a one-off game and the fans are split down the middle, the atmosphere will be different to a league game.
"The fact we played our home games there this season you would think would be a benefit for us but it is the FA Cup semi-final so it will be hard no matter what."
Earlier this season, Spurs registered a 2-0 win when they faced United in the Premier League.