The fire at the Utumishi Girls' Academy Senior School in Gilgil in west-central Kenya broke out in the early hours of Thursday and also injured 79 students.
Students at the school are aged between 15 and 18 years.
Fires are common at Kenyan schools, with many set by students protesting harsh discipline and poor conditions, researchers have found.
"Preliminary investigations have identified eight students as persons of interest in connection with the planning and execution of the suspected arson attack," the police's Directorate of Criminal Investigations said in a statement.
"The eight girls have since been arrested and are currently in police custody."
Education Minister Julius Ogamba told a press conference that preliminary investigations found two teachers at the secondary school had been informed of the students' alleged plans but failed to act to stop them.
The school also failed to observe safety rules, he said, pointing to overcrowding in the dormitories and an emergency exit that was locked during the fire.
As a result, the government has disbanded the school's board of management and will take appropriate legal and disciplinary action against any staff found to have neglected their duties, Ogamba said.
A fire in 2024 at a primary boarding school in central Kenya's Nyeri County killed 21 students. Its cause was never conclusively established.
In the worst school fire of recent times, 67 schoolboys were killed in 2001 at Kyanguli Secondary School outside Nairobi, an incident the authorities attributed to arson.
10°C