SEOUL, South Korea — Park Geun-hye, South Korea’s impeached and ousted president, was sentenced Friday to 25 years in prison, as an appeals court convicted her of collecting more bribes than previously believed from Samsung, the country’s largest business conglomerate.

In a lower-court ruling in April, Ms. Park, 66, was sentenced to 24 years in prison on bribery, extortion, abuse of power and other criminal charges and ordered to pay 18 billion won ($16 million) in fines. But on Friday, the appeals court in Seoul added another year to her prison term and increased her fine to 20 billion won, saying that the collusive ties between Ms. Park and Samsung were more expansive than the lower court had ruled.

Ms. Park, who has been in jail since last year, did not appear in court on Friday to hear the verdict. Her trial does not end until the Supreme Court rules on the case.

Ms. Park’s fall from power began in 2016, when hundreds of thousands of protesters began months of weekly rallies in central Seoul demanding that she be forced from office. That December, the National Assembly impeached her on charges of bribery and abuse of presidential power. In March 2017, Ms. Park became the first South Korean leader removed from office through parliamentary impeachment after the Constitutional Court upheld the lawmakers’ decision.

The case of Ms. Park, a daughter of the former military dictator Park Chung-hee, has exposed the entrenched, collusive ties between powerful politicians and the huge family-controlled conglomerates known as chaebol.

When she was convicted in April, a lower court ruled that Ms. Park and her longtime secretive friend and confidante, Choi Soon-sil, had collected or demanded 23 billion won in bribes from three big businesses, including nearly 7.3 billion won from Samsung.

But on Friday, the appeals court put the amount of bribes Ms. Park and Ms. Choi received from Samsung at 8.7 billion won. It said Samsung offered the bribes to help win government support for an attempt by Samsung’s vice chairman, Lee Jae-yong, to inherit management control from his father, Lee Kun-hee, the company’s chairman.

The ruling on Friday could have legal implications for Lee Jae-yong, who is the de facto head of Samsung, as his father remains seriously ill.

In August of last year, Mr. Lee was sentenced to five years in prison for offering bribes to Ms. Choi and Ms. Park. But he was released from prisonin February after an appeals court cut his sentence in half and suspended it, saying the amount of bribes he offered was smaller, at 3.6 billion won — a finding the judges in Ms. Park’s case disagreed with.

Also on Friday, Ms. Park’s friend, Ms. Choi, was sentenced to 20 years in prison.

The two women were also convicted of coercing 18 businesses into making donations worth 77 billion won to two foundations that Ms. Choi controlled.

The 25-year sentence is not the only prison term Ms. Park faces.

In two separate trials last month, Ms. Park was sentenced to a total of eight years in prison on charges of violating election laws and illegally using millions of dollars from the budgets of the government’s National Intelligence Service.