The sentence last week by Santa Clara County Judge Aaron Persky against former Stanford University swimmer Brock Turner gained international attention after a letter from the athlete's father to the judge that was posted online described the assault as "20 minutes of action."
"Six months for someone who viciously attacked a woman, especially after she was so brave to come forward, is outrageous," Boxer said in a statement.
Asked for a comment on the controversy over his ruling, Santa Clara Superior Court spokesman Joseph Macaluso said Judge Persky is prohibited from commenting on the case because there may be an appeal.
Last week, the victim in the case read a 12-page letter to the court detailing her feelings in the wake of the assault. It was later read millions of times online. The victim's name has not been released to the public.
The uproar over the sentence is part of growing outrage in the United States over sexual assault on college campuses.
In the Stanford case, prosecutors said that witnesses saw Turner, 20, on top of the woman as she lay motionless outside a fraternity party in January 2015. When Turner ran away, two students tackled and held him for police, prosecutors said.
Turner in March was convicted of intent to rape an intoxicated and unconscious person, penetration of an intoxicated person and penetration of an unconscious person. His lawyer said on Tuesday that he was considering appealing the conviction and had filed a notice of intent to appeal with the court.
An online petition at urging the removal of the judge had collected more than 400,000 clicks of support by Tuesday afternoon, in a largely symbolic gesture.
Stanford law professor Michele Dauber has vowed to start a more formal recall effort against Persky, but that is a difficult process rarely used in California.
International interest in the case has led media organizations to request interviews with the woman, but prosecutors said on Tuesday that she wished to remain anonymous.
In a statement released by Santa Clara County Deputy District Attorney Alaleh Kianerci to CNN, the woman said that in addition to wanting to protect her privacy, she could better represent all woman if her name and image were not known.
"I'm coming out to you simply as a woman wanting to be heard," she said in the statement to CNN. "For now I am every woman."
