(FORTUNE Magazine) – July's rally around Internet stocks added two new names--Jerry Yang and David Filo--to America's growing list of Gen X billionaires.

The recent stock runup helped the 29-year-old Yang, a Yahoo co-founder, cross the billion-dollar mark on July 6. Filo, his 32-year-old partner, had been waiting for him across the ten-digit divide since July 2, the day Yahoo closed at 172 7/8. And Amazon.com's 34-year-old founder, Jeff Bezos, beat both the Yahoo boys to the punch in early June, then hit double-billionaire status on June 25. (For more on Bezos and Amazon.com, see Fortune Investor.)

Though Bezos seems securely entrenched, the Yahoo duo's status in the Buffett-and-Gates club is still a tad shaky: A stock stall that started on July 7 threatened to send them back to centimillionaire-hood, but at the time FORTUNE went to press, they maintained their new state of grade-A, three-comma luxe. (Jealous losers take note: Yang falls below the billionaire line if Yahoo dips below $174, Filo when it goes below 171 1/2; Bezos is out when Amazon.com sells below $50.)

Net stock skeptics can always reaffirm their world-view with the story of Jim Clark, the 54-year-old granddaddy of all Internet billionaires. Clark went billionaire in 1995 in the wake of Netscape Communications' hysteria-fueled IPO, when the stock climbed from a split-adjusted $14 to a peak of $86 per share. Three years later, with shares selling at $39, Clark's only worth a lousy $594 million. Poor guy.

--Jane Hodges