Production on the 13 new hours of the dramedy about a secret community of geniuses is expected to begin in Vancouver, Canada, early next year for a summer 2008 premiere.
Returning for season three are stars Colin Ferguson, Salli Richardson, Joe Morton, Jordan Hinson and Ed Quinn.
SCI FI has also renewed its investigative reality hit, "Destination Truth," for a second season to air next year.
In the show, adventurer Josh Gates searches for answers to some the world's most notorious unexplained mysteries.
"'Eureka' rose to an even higher creative level in its sophomore season, combining entertaining, compelling stories with deeper character development and great cast chemistry. And clearly the audience noticed, bringing millions of new viewers to the channel," Mark Stern, SCI FI Channel's executive vice president of original programming, said in a statement.
"'Destination Truth' with Josh Gates proved to be a great addition to our Wednesday night lineup and the perfect companion piece for 'Ghost Hunters.'"