Bill Gates (left) and Warren Buffett

Microsoft founder Bill Gates remains the richest American for the 19th year running on the Forbes' 400 list released Wednesday.

Gates held on to the top position with assets of US$66 billion, up $7 billion from last year due to a 20-percent hike in the price of Microsoft shares and profits from investments in bonds and hedge funds.

Investor Warren Buffett came second with $46 billion, also up $7 billion on stock gains. Oracle CEO Larry Ellison came third, and brothers Charles and David Koch, the secretive owners of the U.S.' second largest privately-held company Koch Industries, shared fourth place.

Four people from the Wal-Mart owner family -- Christy, Jim, Alice and S. Robson Walton -- filled sixth to ninth place. Bloomberg owner and New York Mayor Michael Bloomberg ranked 10th.

Two Korean immigrants, Chang Do-won and his wife Jin-sook, the founders of fast fashion brand Forever 21, featured in the top 100, coming 79th with assets of $4.5 billion. Their wealth increased by $900 million from a year ago and the couple moved up nine places in the ranking.

But Facebook CEO Mark Zuckerberg, who was in 14th place last year, saw his ranking plummet to 36th after the disastrous floatation of his company, and several other owners of social networking sites disappeared from the list altogether.