Perez put 18-month-old Eli Rojas in 150-degree water, water causing the tot's skin to come off.
But rather than take him to a doctor, along with his sister Patricia and her husband Jose Gamez, they drove to a drug store to get ointment.
It was only after the baby had a seizure that they sought medical help.
Alameda County Deputy District Attorney Stacie Pettigrew said it was the worst case she'd ever taken to trial
She said: "Eli was placed in 150-degree water for a matter of a few
seconds. He was burned from belly button down to his toes. All of his skin came off almost immediately. "
She added: "The baby would have been in unimaginable agony as they drove around taking their time trying to cover it up."
Patricia Perez and Gamez were convicted last year of being accessories and received probation.
Reports say Christian Perez had been angry at the child for soiling himself.
The jury, some of whom broke down during the trial, convicted him of torture, second-degree murder and child abuse in the scalding death of his girlfriend's baby.
The Oakland Tribune reports that Perez is scheduled to be sentenced on March 25.