Facebook founder Mark Zuckerberg donated 18 million shares of Facebook stock on Tuesday to the Silicon Valley Community Foundation. The gift is worth half a billion dollars and is Zuckerberg’s largest to date.

The donation may be the largest ever by a Silicon Valley donor to a local charity. Silicon Valley billionaires are known for giving money outside of the area — or not at all.

The gift by Zuckerberg, 28, and his wife, Priscilla, is earmarked for health and education programs. He previously pledged $100 million to schools in Newark, N.J. Mrs. Zuckerberg taught fifth-grade science at San Jose’s Harker School until 2008.

In a Facebook post, Zuckerberg wrote: “Today, in order to lay the foundation for new projects, we’ve made a contribution of 18 million Facebook shares to the Silicon Valley Community Foundation. Together, we will look for areas in education and health to focus on next. I’m hopeful we’ll be able to have as positive an impact in our next set of projects.“

According to a 2007 brief on education in Silicon Valley posted to the foundation’s website, its initiatives include high school reform, removing barriers to postsecondary education and a focus on preschool programs.

The foundation’s education strategy seeks both to improve instruction at schools as well as expand opportunities to learn outside of schools. “Our region is a global hub of technological innovation and discovery. However, a majority of our students are not adequately prepared to contribute to the workforce that is the region’s economic engine,” the foundation said in an introduction to its 2012 call for grants related to education, which announced a strategy “to close the middle school achievement gap in mathematics that separates low-income students and students of color from others in preparing for college and future success.”

The foundation had $2 billion in assets under management before the gift. “Mark’s generous gift will change lives and inspire others in Silicon Valley and around the globe to give back and make the world a better place,” Silicon Valley Community Foundation CEO Emmett D. Carson said in a statement.

Silicon Valley Community Foundation calls itself “a leading voice and catalyst for innovative solutions to the region’s most challenging problems.”  Active in San Mateo and Santa Clara counties, the foundation seeks to improve the region’s quality of life through grantmaking, community initiatives and research.