Stripe founders Patrick and John Collison are worth $11.5 billion (€9.65 billion) each following their company's latest fundraise, according to Bloomberg.
Its Billionaires index, a ranking of the wealthiest men and women in the world, puts them among the richest self-made millennial billionaires.
The Irish brothers, who are aged 32 and 30, were previously valued at $4.3 billion each, according to the index. Forbes magazine had more conservatively estimated their worth to be $2.3 billion prior to this week’s fundraise.
Last week, Stripe, the online payments company they founded in 2010, raised a further $600 million, giving it a market valuation of $95 billion. This makes Stripe the most valuable company in Silicon Valley and among the most valuable globally.
The Ireland Strategic Investment Fund (Isif) was one of the primary investors in the latest fundraise. Stripe said on Sunday it is to create more than 1,000 jobs in the Republic over the next five years. The company currently employs about 2,500 globally, of which 300 are in Dublin.
Stripe handles hundreds of billions of dollars in transactions each year for its clients, which includes many well-known brands.
Snap founders Evan Spiegel and Bobby Murphy, as well as Chinese toy tycoon Wang Ning, are the only other self-made billionaires outside of the Collison brothers under the age of 35 among the world's 500 richest, according to Bloomberg.
British aristocrat Hugh Grosvenor and Walmart heir Lukas Walton hold the sole inherited fortunes in the group of billionaires aged 35 and under.
Bezos on top
Amazon founder Jeff Bezos tops the Bloomberg billionaires index with a $184 billion. He is followed closely by Tesla and SpaceX founder Elon Musk on $180 billion. Bill Gates ($140 billion), LVMH chief executive Bernard Arnault ($127 billion) and Mark Zuckerberg ($108 billion) round out the top five wealthiest people globally currently. Patrick and John Collison are ranked in 197th and 198th spot respectively in the index.
Ahead of them is construction magnate, Pallonji Mistry, the Indian-born Irish citizen who controls engineering business, Shapoorji Pallonji Group and holds a stake in Tata Sons, one of India's biggest businesses. He is ranked in 52nd place with a $27.2 billion fortune.
John Grayken, founder of Dallas, Texas-based private equity business, Lone Star Funds and an active investor in the Republic, is 286th on the list with $8.7 billion. Originally from Boston, Massachusetts, Mr Grayken became an Irish citizen in 1999.