Google's share price topped $500 for the first time yesterday as Wall Street put aside qualms about excessive valuations that have dogged the stock for nearly a year and looked to another burst of growth from the world's biggest internet company.

The latest surge in Google's shares, which have jumped by 37 per cent from a summer low point, caps the company's emergence as chief rival to Microsoft and confirms how far its fortunes have eclipsed those of Yahoo.

At $153 billion, Google's stock market value has risen to more than half that of Microsoft, while its fast-growing revenues and cash flow already equal a quarter those of the tech industry's most profitable company.

The latest rally means it is worth more than four times as much as Yahoo, which has struggled this year to build a search engine advertising system capable of keeping pace with Google.

While analysts cautioned that breaking the $500 barrier did not in itself mark a meaningful change in how investors view the company, it has symbolic value after a year in which Google's stock price lost momentum.

While the shares have jumped more than five-fold since its initial public offering, its rapid growth since then has allowed it to "grow into" its valuation, according to an analyst at Jefferies in New York.