The Warriors also said Monday they have waived guard Raja Bell to reduce their roster to 15 players.
Williams has appeared in 11 games with Golden State. He is averaging 12.8 points, 3.4 rebounds and 2.3 assists per game.
He had signed two 10-day contracts with the team after being a free agent call-up from the NBA Development League. The Warriors needed to sign him for the rest of the season or let him go.