A US woman accused of killing her baby in a microwave oven has been arraigned on murder charges that could lead to the death penalty if she is convicted.

Prosecutors today charged Ka Yang, 29, with one count of murder with the special circumstance that the killing was intentional and involved torture, which would make her eligible for the death penalty or life in prison without parole, the Sacramento Bee newspaper reported.

Ms Yang did not enter a plea when she appeared in court today. 

Authorities found Ms Yang’s six-week-old daughter, Mirabelle Thao-Lo, dead in the family home in Sacramento on March 17.

Officials say the child suffered “extensive thermal injuries”. 

The girl was burned from head-to-toe, but authorities could not find an obvious source for the burns when they arrived at the home, according to the affidavit written by Sacramento Police Detective Thomas Shrum.

The infant’s pyjamas and hair were not singed. A dummy, however, was found in the microwave, Detective Shrum said. 

Ms Yang initially told investigators she blacked out while working on the computer with Mirabelle in her arms and woke up on the ground with the baby injured next to a space heater.

Although Ms Yang had a history of seizures, paramedics did not find her to be disoriented when they arrived, according to the affidavit.

When detectives pointed out inconsistencies in her story, Ms Yang later acknowledged she lied and said she might have a split personality, the affidavit said.

In the months after the infant’s death, police interviewed Ms Yang’s family and co-workers as well as pathologists who have worked on microwave burn cases.

They have not established a possible motive.

“Nothing (Ms Yang) gave us explained what led up to the baby being killed,” police spokesman Norm Leong told the Bee.

Ms Yang was arrested last week after a months-long investigation into what caused the baby’s severe burn injuries.

Ms Yang’s lawyer, Linda Parisi, told reporters after the hearing that her client might have psychological issues.

The woman’s other three children, all under age seven, were removed from the home the day their sister was found dead. They are now living with relatives.