The 22-year-old is Turkish-born but represented die Mannschaft throughout his youth career and has four caps with the senior team to date.
The BVB star told Ntvspor: "It was one of the most difficult decisions of my career.
"I grew up in Germany and went to school there. Also, I started to play football in Germany.
"Two days after the Germany's invite, Turkey invited me too. I decided to choose Germany and then they called me up to play against Belgium in my first match."
Gundogan also exclaimed that there has been interest from clubs in Turkey but insists that he is currently extremely happy under head coach Jurgen Klopp, and also claimed he would turn away English and Spanish overtures, for now at least.
"Three big Turkish clubs wanted to sign me but I refused them," he said.
"One day I want to play in La Liga or the Premier League but now I'm happy and I want to play for Dortmund until 2015.
"I'm very happy to work with Jurgen Klopp. He is like my father."