Microsoft market cap surpasses $US500 billion

Microsoft's market valuation topped $US500 billion today, as its shares jumped more than $5 to close at $99.44.

Market valuation, also called market capitalisation, is calculated by multiplying the number of outstanding shares a company has by its share price. Microsoft had 5,103,859,232 shares outstanding on April 30, according to a recent regulatory filing.

The company's shares rose on published reports that Microsoft plans to create a new stock to track its Internet-related properties, including the Microsoft Network. A company spokeswoman refused to confirm the reports, saying Microsoft doesn't comment on rumours. The software maker also prevailed earlier today in a private antitrust case filed against it by software maker Bristol Technologies.

Microsoft's shares reached a high of $US99.88 in afternoon trading on the Nasdaq stock exchange, up from yesterday's closing price of $94.38, before closing at $99.44.