U.S. District Court Judge Jeremy Fogel inspected the facility to help him decide whether to resume executions by lethal injection in California.
He put them on hold 5 years ago, saying the old death chamber was too dim and cramped to humanely carry out an execution.
Prison officials say the new chamber is roomier and better lit. The state also has adopted new regulations and improved staff training.
Fogel says he will hold several hearings before he rules on the issue.