Holtby signed for Spurs in January from Schalke.
"Everything I hoped for has come true. I had a really enjoyable second half of the season here, although it was more of a meet and greet really because everything happened so quickly, on my second at the Club I made my debut at Norwich!" he told tottenhamhotspur.com.
"The time flew by. It really has been an unbelievable spell, the atmosphere at the Lane is fantastic and it’s been a great experience for me.
"I really enjoyed playing with the lads. 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. We had a great season and we’ll improve."