Yu Wei Gong was charged with murder after he called police in 2017 to turn himself in after a suicide attempt.

He admitted killing his mother Liu Yun Gong about six months earlier, according to court documents. When officers asked where his mother was, he said "in the fridge."

An officer searched the freezer and found human remains, including two arms with hands and a decapitated head, in numerous plastic trash bags, court documents said.

Last year, he pleaded guilty to manslaughter, avoiding a life sentence. His defence attorney and the prosecutor in the case said it's a deal the victim's family supports.

Gong, 28, spent most of Monday's sentencing looking down. He spoke quietly as he apologised to his family in China and Hawaii. "I am ashamed for what I did," he said. "I'm sorry, Mom."

Gong feels he doesn't deserve the forgiveness his family has given him, said Darcia Forester, his public defender.

"I want to make clear that he did love his mother and she was a very good mother," she said. "Under no circumstances did she deserve what happened."

Judge Paul Wong noted the "obviously sensational facts" in the case, even though there was no mention of the gory details.

Wong sentenced Gong to 20 years for manslaughter and 10 years for identity theft, to be served separately. A one-year sentence for abuse of a corpse is to be served at the same time.

The identity theft charge stems from Gong paying rent with his mother's cheque account.

Australian Associated Press