Federer, the reigning two-time Open champion who has never lost to the 25-year-old Russian in seven matches, is 60-1 on hard courts in North American since summer 2004. The match will be Davydenko's first U.S. Open semifinal.
Roddick, the ninth-seeded American who won the U.S. Open in 2003, is in his second semi in four years. Youzhny, 24, beat second-seeded French Open champion Rafael Nadal to reach the semifinals.
The winners meet in the men's final Sunday at center court at Arthur Ashe Stadium.