After reviewing SunPower's (NASDAQ:SPWR) first-quarter results, I couldn't help being reminded of the Greek myth of Icarus -- the son of Daedalus who didn't heed his father's advice about flying too close to the sun on wings fashioned of feathers and wax and plunged to his death.

Investors have every right to be pleased with SunPower's early performance. First-quarter revenues increased 92% over the previous quarter to $143 million, while earnings came in at $1.2 million, or $0.02 a share. Excluding one-time charges, the company pulled in $0.29 a share.

The company sees revenues at $150 million to $160 million for the second quarter and $680 million to $700 million for the year. For fiscal 2008, revenue is expected to increase to $1 billion.

On the operations side, things look just as promising. SunPower's acquisition of PowerLight is proceeding smoothly. Recently, the company -- along with General Electric (NYSE:GE) -- outfitted an 11-megawatt solar plant in Portugal capable of powering 8,000 homes. And on Monday, Tiffany (NYSE:TIF) announced that it would be installing a total of 1.3 megawatts worth of SunPower solar modules on the rooftops of two of its distribution warehouses.

Furthermore, as I mentioned last week, SunPower is continuing to make great strides in improving the efficiency of its solar cells. Combine this with the fact that it has also locked up a steady supply of silicon through 2008, and there is every reason to believe the company will be able to continue to improve its gross margins.

But here's the rub: All of this progress is priced into the stock. SunPower's trailing P/E, based on GAAP, stands at 164, versus 56 for Rule Breakers pick Suntech Power (NYSE:STP) and only 22 for Kyocera (NYSE:KYO).

Of course, with the type of growth SunPower is experiencing, investors prefer the more whimsical forward P/E ratio based on 2007 estimates. But here again, Kyocera -- one of the largest solar companies in the world -- comes in far below the others with a ratio of 22.5. Suntech and SunPower's are at 33.9 and 60.3, respectively.

It is, of course, possible that SunPower will continue to grow well beyond 2008, but, at the risk of sounding like Daedalus warning his son about getting too close to the sun, I believe SunPower investors need to think long and hard about how much higher this stock can go. From my perspective, its stock has already reached the point where its feathers and wax might soon start to come loose and the price might drop for a prolonged time.

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Fool contributor Jack Uldrich doesn't like plunges, and that's why he has never tried bungee jumping. He owns stock in Suntech Power. The Fool has a strict disclosure policy.