Warren Buffett, left, Melinda French Gates and Bill Gates in 2006 after Buffett said he would make an annual donation the Bill & Melinda Gates Foundation. ((Associated Press Photo/Bill and Melinda Gates Foundation, Diane Bondareff))

Investor Warren Buffett has made his annual gift of Berkshire Hathaway stock to the Bill & Melinda Gates Foundation, turning over about $1.5 US billion worth of stock.

According to a Thursday filing with the Securities and Exchange Commission, Buffett donated 19.34 million Class B shares of the company's stock.

The closing price of Class B shares on Thursday was $77.77.

The gift is the fifth installment in Buffett's plan to transfer the majority of his wealth to the Seattle-based foundation run by the Microsoft Corp. co-founder and his wife. The foundation is the world's largest with an endowment of $37.1 billion as of March 31.

Berkshire Hathaway. based in Omaha, Neb., owns a mix of more than 60 companies, including insurance, furniture, carpet, jewelry, restaurants and utility businesses.