Five

• Frederick Ramsdell, an alumnus of UCLA and UC San Diego, who shared the Nobel prize in medicine 
• UC Berkeley professor emeritus John Clarke, who won in physics
• UC Santa Barbara professor Michel H. Devoret, who won in physics
• UC Santa Barbara professor emeritus John M. Martinis, who won in physics
• UC Berkeley professor Omar Yaghi, who won in chemistry 

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Source: https://www.sfchronicle.com/california/article/uc-nobel-prizes-record-21094964.php; https://edsource.org/updates/uc-system-wins-five-nobel-prizes-in-one-week-breaking-a-world-record.