The 22-year-old German international arrived at White Hart Lane from Schalke 04 in January and went on to make 17 appearances during the second part of the campaign.
"I really enjoyed playing with the lads," Holtby told the club's official website.
"There is so much quality here and it's a fight for places because the whole squad is so competitive. It's so enjoyable playing football with these guys."
Tottenham start the new Premier League season with a short trip to Crystal Palace on August 17.