A jury in May recommended the death penalty for Chester Turner, and Superior Court Judge William R. Pounders on Tuesday agreed.
"I don't think any jury would arrive at a different conclusion and would, in any court, demand a death penalty," Pounders said.
Turner, 40, declined to say anything in court after several of the victims' relatives spoke at the hearing. The case will automatically be appealed.
Prosecutors said Turner preyed upon prostitutes and other impoverished women with drug problems who lived primarily in South Los Angeles.
He was convicted April 30 of 10 counts of first-degree murder, plus one count of second-degree murder for the death of one victim's fetus. That victim, Regina Washington, 27, was 6 ½ months pregnant when Turner strangled her with an electrical cord behind a vacant house in September 1989.
Another victim was found slumped over a portable toilet, and one woman was found in front of a crack house.
Turner was already serving an eight-year prison sentence for the 2002 rape of a woman on Skid Row when his DNA linked him to the 10 killings, carried out between 1987 and 1998.