What: Shares of semiconductor assembly and test services provider Amkor (NASDAQ:AMKR) jumped on Tuesday following the company's third-quarter results. Despite a revenue decline, the company beat analyst estimates for both revenue and earnings. At 12:30 Tuesday afternoon, the stock was up about 13%.

So what: Amkor reported quarterly revenue of $734 million, down 9.7% year-over-year but about $9 million higher than the average analyst estimate. Revenue from both advanced products and mainstream products declined year-over-year, with the total number of packaged units falling by 11%.

Amkor reported earnings of $0.12 per share, down from $0.20 in the same period last year but $0.08 better than analysts were expecting. Amkor attributed the earnings beat to favorable exchange rates, as well as a richer mix of assembly and test services. Gross margin declined by 1.6 percentage points year-over-year to 17.2%, but increased from 15.6% in the second quarter. EPS tripled sequentially.

Now what: While Amkor's earnings were better than expected, the company's guidance was disappointing. Fourth-quarter revenue is expected to be between $660 million and $710 million, a sequential decline between 3% and 10%, while net income is expected to be between a loss of $0.02 per share and a gain of $0.05 per share.

While shares of Amkor initially fell in after-hours trading following the earnings announcement on Monday, the stock reversed itself on Tuesday. The stock is still down nearly 40% from its 52-week high even after today's rise, so while the company's guidance was lackluster, the bad news may have already been priced in.

Timothy Green has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.