Shares of the online bookseller had increased as U.S. markets opened, and climbed as much as 2.9 percent just before noon in New York on Thursday, giving Bezos a net worth of $92.3 billion.
With investors bracing for the Seattle-based company to report second-quarter results after the close, the shares tumbled.
Gates returned to the top spot when he finished the day with a net worth of $89.8 billion while Bezos followed with $88.8 billion, according to Forbes and Bloomberg.
Bezos quit his job at a hedge fund to start his online bookselling website in a garage in Seattle in 1994.
He first featured on the 400 richest Americans list in 1998, a year after Amazon went public, with a $1.6 billion fortune.
Gates’ first inclusion in the billionaire’s list was in 1982 and he has been no. 1 for 18 of the past 23 years.