NEW YORK (AFP) - Microsoft founder Bill Gates retained his title as wealthiest American, while three founders of online companies joined the top 10, according to the Forbes 400 list released Tuesday.

Mr Gates held onto the number-one spot in the annual list of the 400 wealthiest Americans for the 22nd straight year, with net worth of US$76 billion (S$108.5 billion), down US$5 billion from 2014.

Warren Buffett, the head of conglomerate Berkshire Hathaway, ranked second with US$62 billion, while former Oracle chief executive Larry Ellison is third with US$47.5 billion.

Forbes said the average net worth of the 400 members on the list stands at a record US$5.8 billion, above the US$5.7 billion last year. Total wealth is US$2.34 trillion, up from US$2.29 trillion in 2014.

Entering the top 10 richest rank this year were three founders of e-businesses. Amazon founder Jeff Bezos bolted from 15th to fourth place at US$47 billion, thanks to the surging value of Amazon stock.

Facebook CEO Mark Zuckerberg, who jumped from 11th to seventh place, had net worth of US$40.3 billion. And Larry Page, CEO of Google, moved from number 13 in 2014 to land the 10th spot, with US$33.3 billion.

The business magazine also spotlighted Republican presidential contender Donald Trump, who has claimed wealth of at least US$10 billion. Forbes came up with a lower figure, rating the billionaire in 121st place.

"After interviewing more than 80 sources and devoting unprecedented resources to valuing a single fortune, we're going with a figure less than half that - US$4.5 billion, albeit still the highest figure we've ever had for him," Forbes said.