The trial judge can reduce Rickie Lee Fowler's penalty to life with no parole, the Los Angeles Times reported.
Fowler was convicted in August of five counts of murder and of arson.
The Old Fire in San Bernardino County in October 2003 gutted 1,000 houses and blackened mountainsides over a wide area.
Six men died from heart attacks during the fire, and the jury blamed Fowler for five of them.
Fourteen more deaths were subsequently linked to the fire when a Christmas 2003 mudslide on a hillside stripped of vegetation swept through a church camp. Fowler was not charged with causing the slide.
Prosecutors said Fowler started the fire because he was angry his godfather had thrown him out of his house.
Deputy District Attorney Robert Bullock argued during the penalty hearing that Fowler's violent past of methamphetamine use and of "misery and mayhem" toward others made him a good candidate for execution.
Michael Belter, Fowler's lawyer, said his client did not deliberately kill anyone.
Belter argued Fowler's childhood troubles contributed to his behavior: "How is it that Rickie Fowler got here? When you're 8 years old, you should not be living in filth, or given a line of methamphetamine by your dad."