Samsung has blamed faulty batteries for the fires that led to last year's humiliating recall of its Galaxy Note 7 device.
The batteries had been suspected as the cause but Samsung said on Monday 23rd January that this had been confirmed by internal and independent investigations.
Around 700 researchers and engineers worked on the investigation, testing more than 200,000 devices and more than 30,000 batteries, the company said in a statement.
South Korea-based Samsung recalled 2.5 million Note 7s in September last year after several exploded or caught fire.
At the time, the company blamed the batteries, thought to be made by its sister firm Samsung SDI.
Batteries in the replacement phones were thought to have been provided by China-based ATL.
But after some of these devices also started to catch fire, Samsung killed off the Note 7 completely in October.
The saga severely damaged the company's reputation and cost it billions of pounds in lost profits.
Koh Dong-Jin, head of Samsung's mobile business, said: "We sincerely apologise for the discomfort and concern we have caused to our customers."
In a statement, the company added: "We are taking responsibility for our failure to ultimately identify and verify the issues arising out of battery design and manufacturing.
"The lessons of the past several months are now deeply reflected in our processes and in our culture."
It said it had taken "several corrective actions to ensure this never happens again".