This is the 11th year that Gates has topped the Forbes list.
Once you strip out the five Waltons, the offspring of the founder of Wal-Mart Stores, each of whom is reckoned to be worth US$18 billion, the next two people on the list are also high tech. Michael Dell comes in at No. 9 with US$14.2 billion, and Larry Ellison rounds out the top 10 with US$13.7 billion.
Ellison's standing, in particular, is lower than expected. Last year, he was believed to be worth the same as a Walton, US$18 billion, but the decline of Oracle stock has brought down his net worth.
The new boys on the block, Google founders Sergey Brin and Larry Page, appear on the list for the first time, sharing the 43rd spot with US$4 billion each. The youngest on the list, they are behind the long-established Jeff Bezos of Amazon.com, who holds the No. 38 spot with US$4.3 billion.
The total net worth of the richest 400 Americans topped US$1 trillion for the first time since the height of the dot-com boom four years ago.
Earlier this week, Microsoft revealed that it would keep both Gates' and Ballmer's pay almost static at just over US$900,000 apiece.
Ron Coates of Silicon.com reported from London.