(BLOOMBERG) - Jeff Bezos' net worth reached $105.1 billion (S$140.1 billion) Monday (Jan 8) on the Bloomberg Billionaires Index as Amazon.com shares added to a 12-month surge that's lifted the online shopping giant's market value by almost 57 per cent.

Amazon shares have risen 6.6 per cent this year, with a report showing the Seattle-based company captured 89 per cent of online spending among dominant holiday retailers in the five-week period beginning the day after Thanksgiving in the US.

The latest jump has pushed Bezos' fortune definitively above the high reached by Microsoft's Bill Gates in 1999. The Amazon founder passed Gates in October with a net worth of US$93.8 billion and his fortune crossed US$100 billion for the first time a month later when the holiday shopping season kicked off on Black Friday.

Gates, 62, would have a net worth of more than US$150 billion if he'd held onto assets that he's given away, largely to the Bill & Melinda Gates Foundation. He has given away almost 700 million Microsoft shares and US$2.9 billion of cash and other assets since 1996, according to an analysis of his publicly disclosed giving.

Bezos also controls closely held space exploration business Blue Origin and the Washington Post.