The 'Fast & Furious' star was involved in a fiery car crash in Valencia, California last month, when the Porsche his business partner Roger Rodas was driving crashed into a tree and burst into flames.
Walker's death certificate confirms he was not killed by the impact of the crash alone, but was burned to death once the car exploded, reported TMZ online.
The Los Angeles County Coroner said that Rodas died from "multiple traumatic injuries", but unlike Walker, the fireball which engulfed the vehicle was not a factor in his death.
Walker was laid to rest following a private funeral service at the Forest Lawn Memorial Park in the Hollywood Hills on Saturday.
Over 200 friends and family were in attendance, including his parents, Paul and Cheryl Walker, brothers Caleb Walker and Cody Walker, and 'Fast & Furious' co-stars Tyrese Gibson, Ludacris and Michelle Rodriguez.