She joins billionaires such as investor Warren Buffett and Microsoft founder Bill Gates in the Giving Pledge.

The pledge was started by Mr Buffett and Mr Gates and calls for the richest to give away half or more of their wealth.

Ms Bezos is estimated to be worth almost $37bn (£29bn). She and Mr Bezos divorced earlier this year.

"In addition to whatever assets life has nurtured in me, I have a disproportionate amount of money to share," she said in a statement. "My approach to philanthropy will continue to be thoughtful. It will take time and effort and care."

The Giving Pledge has been signed by 204 individuals, couples and families from 23 countries.

Former New York Mayor Michael Bloomberg, CNN founder Ted Turner and entertainment executive Barry Diller were among the initial signatories in 2010.

Pledges this year have come from hedge fund billionaire Paul Tudor Jones; Jeremy Grantham, who is co-founder of US investment firm GMO; and Emirati businessman Sheikh Mohammed bin Musallam bin Ham Al Ameri.

Public promise

The pledge is a public promise rather than a legal contract, according to its website, which says: "The goal is to talk about giving in an open way and create an atmosphere that can draw more people into philanthropy."

Mr Bezos is not one of the signatories to the Giving Pledge. Last year, he put $2bn into a charitable fund he established to help the homeless and set up a new network of schools.

He is estimated by Bloomberg to be worth $114bn.

Other top-10 billionaires who have not joined the pledge are Google co-founder Larry Page, Bernard Arnault, head of French luxury goods conglomerate LVMH, and Mexican telecoms chief Carlos Slim.