Indian-American Silicon Valley venture capitalist Vinod Khosla and his wife Neeru have pledged half of their vast fortunes to charity either during their lifetime or after death.

Ten more families, including the Khoslas, signed the pledge on April 28, bringing the total number of signatories to 69. Many of Silicon Valley's leading entrepreneurs, including venture capitalist John Doerr, Oracle chief executive officer Larry Ellison, hedge fund manager Tom Steyer and Facebook creator Mark Zuckerberg, had signed on to the pledge.

“I am delighted that so many wealthy Americans are taking a public pledge that supports philanthropy,” Warren Buffett, pledge co-founder and chairman and CEO of Berkshire Hathaway, said in an April 28 statement.

Mr. Khosla (56) is Silicon Valley's most prominent “green” venture capitalist. A co-founder of Sun Microsystems, Mr. Khosla was a general partner at venture capital firm Kleiner Perkins Caufield & Byers before striking out on his own with Khosla Ventures in 2004.

The Sand Hill Road firm focuses on cleantech and information technology start-ups, with a portfolio that includes carbon sequestration and storage, solar, batteries, biofuels, building materials, energy efficiency and next-generation lighting and appliance companies.

As of March, Mr. Khosla's net worth was $1.4 billion, according to a calculation by Forbes.