The 22-year-old has played in a number of positions for his country, but he will start Saturday's showdown at full-back.
"For me, it is a dream come true," he said. "I have always wanted to play full-back for my country and what a time to do it, in the quarter-final of the World Cup. I couldn't wish for more.
"I am really pleased to be picked there and to be given an opportunity. I want to take it with both hands."
Halfpenny has made 22 appearances for Wales.