Move Over, Microsoft: Apple Becomes Most Valuable Public Company Of All-Time

The Cupertino, Calif.-based iPhone maker reached a record market capitalization of $623 billion Monday afternoon, the highest of any publicly traded company in history. Apple stole the crown from fellow tech giant Microsoft, which had held the record for 12 years after reaching $620.58 billion in December 1999.

The record was set after Apple stock surged to a record $664.74, before dropping slightly to $661.7 Monday afternoon.

[Related: Apple Nabs 70 Percent Of Global Tablet Market ]

Anticipation of the upcoming iPhone 5, which Apple is reportedly unveiling September 12, is likely the driving force behind the spike in its stock. The new phone is expected to be thinner and faster compared to the four prior-generation iPhones, and also run iOS 6, Apple's next-generation mobile operating system. Support for 4G LTE networks and near-field communications technology are also widely expected.

Reports have also surfaced suggesting Apple is prepping a lower-cost, 7-inch iPad for the end of the year, another factor fueling its rising stock.

Apple's market cap surpasses the $405 billion held by Exxon Mobile, the world's second most valuable company, by more than $200 billion or nearly 53 percent.

According to Jefferies analyst Peter Misek, shares of Apple will continue to climb, reaching the $900 mark upon the launch of the iPhone 5, a release he expects to be "the biggest handset launch in history," the Wall Street Journal reported.