Williams-Goss said he has achieved his goals of earning a college degree, improving his game and helping Gonzaga reach the Final Four.
The guard played his first two seasons at Washington, then sat out a year per NCAA rules before leading Gonzaga to a 37-2 record.
He was named West Coast Conference player of the year and newcomer of the year.
"Coming to Gonzaga is the best decision I ever made," said Williams-Goss, who is from Happy Valley, Oregon.
He is considered most likely to be a second-round pick or free agent.
In addition to leading the Zags in scoring, Williams-Goss averaged 6 rebounds, 4.7 assists and 1.7 steals per game. He shot nearly 87 percent from the free-throw line.
Williams-Goss reached double digits in scoring 32 times and was named to the all-tournament team at the Final Four.
He had a 3.84 GPA in psychology and had started work on a master's degree.
"What I was most surprised by this season was not the wins, awards or recognition, but rather the genuine love I felt with our fans in Spokane," Williams-Goss wrote on Instagram .
He said he was 100 percent confident in his decision to try for the NBA.
"I am prepared both mentally and physically to take this step in my career and my life," he wrote.
Guard Josh Perkins and forward Johnathan Williams are the sole returning starters for the Zags. Also back are veterans Silas Melson and Killian Tillie.
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