Queenie Rosita Law, granddaughter of late textiles tycoon Law Ting-pong, who founded the Bossini clothing chain, was abducted from her house in Hong Kong in April last year.
The 29-year-old was held in a mountain cave for four days before family members paid a ransom of Hong Kong Dollar 28 million (USD 3.61 million) for her release. Most of the gang fled to mainland China afterwards, where they were captured.
Ringleader You Dunkui was sentenced to 15 years for kidnapping, with the others being given terms ranging from 13 years to just under two, he said.
Another gang member, Zheng Xingwang, was sentenced to 12 years by a Hong Kong court last month, having admitted to forcibly taking or detaining a person with intent to procure a ransom.
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Law and her boyfriend were asleep at her house in the quiet coastal area of Clearwater Bay when a gang of six mainland Chinese men raided the house, tied them up and taped over their mouths, Zheng's Hong Kong trial heard.
She was tied to one of the gang members, who carried her on foot to a hillside cave 90 minutes' walk away while the boyfriend was told to notify her father of the ransom demand.
Hong Kong police embarked on a massive operation to hunt down the suspected kidnappers, deploying hundreds of heavily armed officers, helicopters and marine vessels, and setting up roadblocks.
Almost all of the money has been recovered, including some buried on hillsides near the cave where she was taken.