Klemmer, who tips the scales at 120kg, is yet to play an NRL game, but is rated as one of the most promising forwards in the game and was named player of the year in the NYC under-20s competition in 2012.
The 19-year-old had come through the club's development system and is set to make his first-grade debut against North Queensland in Gosford on Saturday.
"I've been at the club for a number of years now and I couldn't see myself anywhere else in this next period of my career," Klemmer said.
"I've learnt so much and I enjoy every day that I come here, I'll keep working hard and learning from Des and the other players here and hopefully I will get my chance at some stage to play NRL."
Bulldogs coach Des Hasler is excited about being able to retain the young forward.
"We're excited to have re-signed David for the next three years," Hasler said.
"He has been a part of the junior development system for a number of years.
"At just 19, he is an exciting prospect and will provide great depth for the Bulldogs moving forward."