The new deal means the 21-year-old, who joined the Blue and Gold to play Under 20s in 2012, will be with the side until the end of the 2018 season.
Parramatta Eels CEO Scott Seward says Radradra is a welcome re-signing for the club.
"Semi has quickly become a cult figure for Eels Members and fans, and his improvement on the field since he joined the club has been remarkable," Mr Seward said.
"It's great to see the club holding on to key players for the future, and we're delighted to have Semi in Blue and Gold."
Head Coach Brad Arthur said the young winger was still learning in his first full season playing in NRL.
"Semi's an exciting player who is a definite crowd-pleaser and has great finishing abilities," Arthur said.
"He's been working hard to adjust to rugby league since signing with the Eels and he's a valuable part of the side."
Radradra is currently the leading try-scorer in the NRL for 2014, crossing the line 11 times in just 11 games.Like