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.