Amkor Technology (AMKR) shares plummeted 5.79% in after-hours trading on Monday, despite reporting better-than-expected third-quarter results. The semiconductor packaging and test services provider's stock decline appears to be driven by a disappointing fourth-quarter outlook and the announcement of its CEO's impending retirement.

For the third quarter, Amkor reported earnings of $0.51 per share, surpassing the analyst consensus estimate of $0.42 and showing a 4.08% increase from the same period last year. The company's quarterly sales reached $1.987 billion, beating the expected $1.932 billion and marking a 6.71% year-over-year increase. These strong results, however, were overshadowed by the company's forward guidance.

Looking ahead to the fourth quarter, Amkor forecasts earnings between $0.38 and $0.48 per share on net sales of $1.78 billion to $1.88 billion. This outlook falls short of analyst expectations of $0.42 per share and $1.86 billion in revenue, potentially explaining the sharp after-hours sell-off. Adding to investor concerns, the company announced that CEO Giel Rutten intends to retire at the end of the year, with COO Kevin Engel set to take the helm on January 1, 2026. While the company assured a smooth leadership transition, such changes often create uncertainty among investors, contributing to the stock's decline.