MacKenzie Bezos ha vowed  to donate than half of her fortune to charity as part of the Giving Pledge, the organization said Tuesday. Ms. Bezos, whose divorce from the Amazon founder and chief executive Jeff Bezos made news earlier this year, was among 19 new signatories announced by the group.

“I have no doubt that tremendous value comes when people act quickly on the impulse to give. No drive has more positive ripple effects than the desire to be of service,” Ms. Bezos, a novelist, wrote in a letter.

Once the devorce ends in July, Ms. Bezos will own a 4 percent stake in Amazon, with shares worth about $36 billion. Mr. Bezos kept most of the couple’s shares, or about 12 percent of the company.

The value of the company on Tuesday is about $907 billion, meaning that Mr. Bezos, with a $108 billion stake, remains the richest person in the world, just ahead of Bill Gates.

In 2018, Mr. Bezos and Ms. Bezos promised $2 billion for a fund to start preschools and help homeless families.

In 2017 Mr. Bezos and Ms. Bezos jointly announced the dissolution of their marriage.

“After a long period of loving exploration and trial separation, we have decided to divorce and continue our shared lives as friends,” the statement read. “We’ve had such a great life together as a married couple, and we also see wonderful futures ahead, as parents, friends, partners in ventures and projects, and as individuals pursuing ventures and adventures.”