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 Amkor Technology (NASDAQ:AMKR) are up by over 10% today after beating expectations on both top and bottom lines in its first-quarter earnings report.

So what: Amkor's revenue rose 5% year over year, to $688 million, which easily beat the $672.4 million consensus. Earnings of $0.07 per share also came in well ahead of the $0.03 consensus. Guidance also appears favorable, as Amkor now expects between $730 million and $780 million on the top line, and between $0.09 and $0.19 in EPS, against consensus estimates of $719.4 million and $0.11 per share, respectively.

Now what: Even after the pop, Amkor's valuation seems reasonable, and its growth prospects are such that the forward P/E is under five at the moment. The only real area of concern is Amkor's wide margin of error in its second-quarter guidance, which, despite representing a solid advance on even the low ends, could indicate a bit of uncertainty. It's certainly worth a second look, and this good news might even start to reverse a long-term downtrend that's plagued Amkor shareholders for years.

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Fool contributor Alex Planes holds no financial position in any company mentioned here. Add him on Google+ or follow him on Twitter @TMFBiggles for more insight into markets, history, and technology.

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