The new deal will keep Hamer at the Madejski Stadium until the summer of 2012.
Hamer’s previous deal was due to expire a tthe end of the season.
“I want to prove to everyone I’m a good goalkeeper and I’ve not had a run of games to do that here yet,” he told the club’s official website.
“And that’s why I’ve signed a new contract. Reading is a great club and I’d love to be able to make my impression on the first team.
“Feds has been fantastic and is proving to be a difficult man to budge, but that’s part of football. The club believe in me, but now I have to prove I’ve got a lot to offer.
“To keep my match sharpness I’ve been playing regularly at Brentford and it’s a great feeling.
“So now, I’m looking forward to playing well whilst on loan and then coming back here when I’m needed and cracking on.”
Reading director of football Nick Hammond added: “I’m very pleased Ben has signed.
“He is continuing to develop and is still young, especially for a goalkeeper.
“He’s done very well back on loan at Brentford in the past few weeks, and already has a lot of games under his belt in his career.”