Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of semiconductor equipment company Mattson Technology (Nasdaq: MTSN) slipped as much as 25% after the company lowered its guidance for the fourth quarter.

So what: Mattson's original fourth-quarter guidance called for revenue in a range of $46 million to $50 million and net loss per share between $0.04 and breakeven. The revised expectations put revenue at $41 million and simply said that the net loss per share would be "significantly greater" than previously expected. The company blamed the disappointment on continued weakness in the DRAM market, though it remained optimistic about an overall recovery in the semiconductor industry.

Now what: On the bright side, Mattson continues to maintain a solid, debt-free balance sheet. The company also stands to see an upswing in its results if the recovery in the semiconductor industry continues. However, the company's historical financial performance doesn't paint a terribly compelling picture, so it's hard to consider the stock much more than a speculation at this point. Looking out more broadly, the miss by Mattson may be good reason for investors to keep a close eye on other semiconductor equipment makers like Applied Materials (Nasdaq: AMAT) as well as major DRAM players like Micron Technology (NYSE: MU).

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy is looking forward to a great 2011!