The German established himself as Martin Jol's first choice at right-back last season, while on loan from Cologne, and he signed a permanent deal back in May.
Riether, who was named player of the year by his team-mates, played 39 times in his first season in England and grabbed his first goal in their 2-2 draw with Sunderland in March.
"I'm happy to have got the deal done," Riether told Fulham's official website.
"I like it here - I love Fulham, I love the fans, I love the club, and I'm happy that we could close this deal now.
"It's the start of the season and we are well prepared so I'm looking forward to the future."