Mark Zuckerberg probably likes Forbes today: the magazine has named him the 35th richest – as in most valuable – person in the US, passing Steve Jobs (42nd) and Rupert Murdoch (38th) on the way.

The co-founder of Facebook, aged 26, is estimated to be worth $6.9bn (£4.4bn), based on his shareholding in the social networking site, which boasts 500 million members worldwide.

The value is calculated based on recent investments in his company by outside businesses in return for shares. That has tripled since last year – the largest relative increase on this year's Forbes US rich list.

The complete Forbes list of the 400 richest people in the US is topped, as it has been for years, by Bill Gates, the co-founder of Microsoft, who has since left it to carry out charitable work in the developing world. His shares in the company are valued at $54bn – up by $4bn from last year.

Zuckerberg is one of only eight members of the US list under 40. Two of the others are co-founders of Facebook – one of them, Dustin Moskovitz, is the youngest on the list, born just eight days after Zuckerberg, and worth $1.4bn. Two others of the under-40 set are the co-founders of Google, Sergey Brin and Larry Page, both worth $15bn and aged 37, making them equal 11th on the list.

The list shows the dominance of technology companies in creating value in the US. Out of the top 50, 13 are in technology companies. After Gates, the third most valuable is Larry Ellison, chief executive of the database company Oracle ($27bn); other technology companies including Microsoft, Amazon (Jeff Bezos, 18th with $12.6bn), Apple (Jobs is valued at $6.1bn from his shares in Apple and Disney Pixar), SAS Institute (which makes business analytics software), Google (Eric Schmidt, the chief executive, is 48th at $5.45bn), eBay (co-founder Pierre Omidyar is 47th with $5.5bn). Murdoch, the News Corp chairman and chief executive, is valued at $6.2bn.

The listing also shows that the stock market has been kind to the billionaires: where last year, a fortune of $950m was enough to get you into the top 400, the entry price has risen again to $1bn. In all, the 400 are worth a total of $1.37tn, compared with $1.27tn last year – an increase of nearly 8%, compared to the stock market's rise of just 1%.

Most benefited from growth in their companies: after a dismal 2009, when 314 out of the 400 saw a fall in their wealth in the wake of the 2008 collapse of Lehman Brothers and the banking crisis, the top 10 this year gained $24.9bn in value (after dropping $40bn in value last year), and 217 of the list are now worth more than a year ago. Only 84 have seen decreases in their calculated wealth.