The German defender moved to Craven Cottager on a season-long deal from FC Koln over the summer.
"For me, it's been a great time at Fulham so far," the 29-year-old told the club's official website. "It was my first experience of another country and it was a big step for me to come to England, but I have to say Fulham is like a family and I like playing here.
"The fans are great, I like the stadium and it's been all good so far."
Riether has made 29 appearances in all competitions for Fulham this season.