Investor Warren Buffett, the head of Berkshire Hathaway Inc., remains in second place with USD 58.5 billion, while Oracle Corp. Co-founder Larry Ellison stays third with USD 41 billion.
Brothers Charles and David Koch, co-owners of Koch Industries Inc., stay tied for fourth with USD 36 billion each.
Forbes says America's super rich continued to increase their wealth over the past year, with the 400 people on the list posting a combined net worth of USD 2 trillion, up from USD 1.7 trillion a year ago.