South Korea's Supreme Court also ordered a new trial for Samsung heir Lee Jae-yong, who was convicted of offences including bribery and embezzlement in connection with the scandal that brought down former president Park Geun-hye.
South Korea's top court on Thursday sent back jailed ex-president Park Geun-hye's corruption case to a lower court for separate trials for her previously convicted charges, a ruling that could increase her already-lengthy prison term.
South Korea's first female president was impeached by lawmakers in December 2016 and officially removed from office in March 2017 over the scandal that triggered months of street rallies involving millions of people.
An appellate court earlier sentenced Park to 25 years in prison over bribery, extortion, abuse of power and other charges.
That was an extension of a 24-year prison term set by a district court.
But the Supreme Court ordered the Seoul High Court to deal with Park's bribery charge separately from other charges.
Local media said Park could face a lengthier prison term because courts handling a case with multiple charges typically don't impose all the maximum sentences for each charge.
Extortion, bribes, and abuse of power
Park was convicted of colluding with a longtime confidante to take millions of dollars in bribes and extortion from businesses, including Samsung, while she was in office from 2013 to 2016.
The two women were also convicted of taking bribes from some of those companies, including more than $6.5 million alone from Samsung.
Park was also earlier convicted of colluding with senior government officials to blacklist artists critical of her government to deny them state assistance programs.
Park was also convicted of passing on presidential documents with sensitive information to Choi Soon-sil via one of her presidential aides.
Park, 67, has called herself a victim of political revenge, has refusing to attend her trials since October 2017 and didn't attend Thursday's court session.
Park, a daughter of late President Park Chung-hee, was once the darling of conservatives in South Korea and dubbed by local media as "Queen of election" for her ability to win tight elections.
Her fall badly smashed conservatives in South Korea and helped her main liberal rival and current President Moon Jae-in win an easy victory in a by-election triggered by her early departure.
Park has been embroiled in two other smaller scandals which led her to be sentenced to two years in prison for violating election law and five years in prison for abusing state funds.
That meant Park has faced the prospect of serving more than 30 years in prison.
The supreme court on Thursday overturned part of an appeals court ruling in the bribery case of Samsung Group's de facto chief Jay Y Lee, who had been given a two-and-a-half-year suspended sentence for seeking favour from Park.
The Supreme Court said the interpretation by the Seoul High Court on what constituted bribes by Samsung to Park was too narrow.
Lee, 51, was initially sentenced in 2017 to five years imprisonment for bribing a friend of Park as he sought to succeed his father and secure control of Samsung Group.
He was freed after a year in detention when the appellate Seoul High Court halved his sentence and suspended it for four years.
Park's friend Choi Soon-sil, was jailed for 20 years, both for bribery and other charges.
The case centres on whether three horses donated by Samsung Group for the training of Choi's daughter, a competitive equestrian, should be considered bribes aimed at winning Park's favour.
Court documents showed Park asked Lee to help the daughter and was convicted on grounds that the horses were bribes worth $3.05 million.
However, the horses were not recognised as such in Lee's trial, helping reduce his sentence.
The ruling comes at a critical moment for both Samsung and its home country, as Japan's decision last month to restrict exports of key chipmaking chemicals following a diplomatic dispute threatens to disrupt the production of memory chips, South Korea's biggest export item.
Lee has since been on a high-profile mission to tackle what he told his lieutenants was a "crisis."
Samsung, the world's biggest maker of memory chips and smartphones, is also facing falling profitability as prices of chips and display panels slide. It reported a 56 percent drop in June-quarter profit and said Japan's curbs blurred its outlook.