The junior posted his decision on his Twitter account Monday.
In a statement released by Washington State later in the day, Franks said he would not yet hire an agent.
"I'm excited at the thought of playing at the next level and want to test out the process and see what opportunities lay ahead for me," Franks said. "I'm not going to hire an agent just yet. I want to get some feedback and see what I can potentially do."
Franks was a breakout star in an otherwise down season for the Cougars. He averaged 17.4 points per game, good for seventh in the Pac-12, and was named the most improved player in the conference. Franks averaged just 6.3 points per game as a sophomore.
Where Franks plays in the NBA will be the question. He's 6-foot-7 with a long wingspan and has improved his outside shooting, making 40.5 percent of his 3-point attempts last season.