The new deal will keep the 22-year-old at Loftus Road until the summer of 2012.
“I’m very happy,” Ephraim told the club’s official website.
“I was in the last year of my contract, so I’m just delighted we’ve managed to get it sorted after a few months of negotiating.
“I’m really enjoying life under the gaffer and I’m playing some of the best football of my career at the moment, so things couldn’t be much better.”
QPR boss Warnock added: “It’s his just reward for his performances.
“We’re building for the present day, as well as the future, and he’s the type of player we want at this football club.
“He loves the game and his enthusiasm is remarkable. He’s a key member of the squad and we’re delighted he’s agreed an extension.”
