Priestland damaged his left shoulder in the quarter-final against Ireland last Saturday, forcing coach Warren Gatland to make one change to the side who beat the Irish 22-10 in Wellington.
Hook will win his 58th cap against the French after getting the nod over Stephen Jones, who will be hoping to make his 103rd appearance for Wales from the bench in the only other change to the matchday squad.
"It's part of sport, isn't it, you pick up injuries," Gatland told a news conference at the team hotel.
"You don't dwell on it, he's not available to us. James Hook gets his opportunity, he's very experienced. We're lucky that we haven't picked up too many injuries in this competition.
"To have someone of the quality and class of James to call on shows what a great position we're in."
Priestland, who made his international debut earlier this year, is one of a young band of players who have helped Wales on a fairytale ride to the last four of the World Cup for only the second time after 1987.
Gatland, who said it was "tough call" to pick Hook over Jones, insisted the absence of the 24-year-old flyhalf would not mean a change to the attack-minded style that has characterised their campaign so far.
"We're not going to change the way we play," the New Zealander said. "We've encouraged the players to make good decisions and if that means moving the ball from the 22, they're encouraged to do it. I think we've played smart rugby..."
Openside flanker Sam Warburton, who has just turned 23, will captain the side and said his team mates were "buzzing with confidence" after last weekend's win over the Irish.
Gatland has often said that the younger players were playing without fear and certainly recent poor track record against the French was not bearing heavily on Warburton.
"I've been involved in the squad to play France twice now and we've lost both, but it's a World Cup and I think anything can happen and that's why this game is wide open and it should be a good one to watch," he said.
"I don't think history counts for anything when it comes to the semi-final of the World Cup."
Gatland said that although his team had "flown under the radar" at the tournament, they had always backed themselves to go deep into the tournament if they got their preparations right.
"We don't think we're quite finished," Gatland said. "Welsh teams, in my experience, are very dangerous when their backs are to the wall ... so we've got a huge amount of confidence."
Team: 15-Leigh Halfpenny, 14-George North, 13-Jonathan Davies, 12-Jamie Roberts, 11-Shane Williams, 10-James Hook, 9-Mike Phillips, 8-Toby Faletau, 7-Sam Warburton (captain), 6-Danny Lydiate, 5-Alun Wyn Jones, 4-Luke Charteris, 3-Adam Jones, 2-Huw Bennett, 1-Gethin Jenkins.
Replacements: 16-Lloyd Burns, 17-Paul James, 18-Bradley Davies, 19-Ryan Jones, 20-Lloyd Williams, 21-Stephen Jones, 22-Scott Williams.