Shares of

Nvidia

(NVDA) - Get Report

tumbled a day after it reported lackluster

financial results and guidance, prompting one brokerage to slap a sell rating on the stock.

In early afternoon trading, the stock was down $2.67 or 18.4%, to $11.88.

Prudential, which downgraded its rating on Nvidia to sell, also saddled the stock with a $9 price target -- implying nearly 40% downside from yesterday's close of $14.55. The firm hasn't done banking for the company.

In a note, analyst Hans Mosesmann suggests the stock has gotten overvalued. Shares of Nvidia have nearly doubled in the past month, soaring 97% from Oct. 9 through the Thursday close. The stock outperformed the

S&P 500

by 81% in just under a month.

Mosesmann calls that run-up "premature" in light of uncertainty in the PC market and the company's own product cycle. Yesterday Nvidia said its flagship NV30 chip won't be available in time for Christmas.

Though the company didn't break out a pro forma earnings number, Mosesmann estimates it delivered about 6 cents a share excluding charges. That's 2 pennies below the Street consensus and at the low end of its own guidance for 6 to 12 cents a share in earnings.

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His new price target assumes a P/E ratio of 15 times his fiscal '04 earnings estimate of 60 cents -- at the bottom end of Nvidia's historical trading range of between 14 and 90 times earnings over the past few years.

UBS Warburg, which also issued a cautious note on Nvidia, said its "hold" rating on the stock is under review, presumably to the down side. The firm has no banking relationship with the company. "In the near term, I think people are concerned about flat growth in its strongest seasonal quarter and uncertainty as to when it will receive the benefit of its new highest-end product," the NV30, says analyst Alex Gauna.

He attributes today's selloff partly to Nvidia's forecast for flat sales in its January quarter, versus Street expectations of 4% growth. "Given that the January quarter is historically the seasonally strongest quarter, when you put that flat it really makes you question 2003," he says.

Wall Street currently anticipates revenue growth of 2% in calendar year 2003, according to Thomson Financial/First Call.