FormFactor (NASDAQ: FORM) experienced a sharp 5.10% decline in after-hours trading on Thursday, in a surprising turn of events following a day of positive news. The semiconductor test equipment manufacturer had earlier seen its shares soar 18.3% during regular trading hours after reporting better-than-expected third-quarter profit and revenue.

The company's strong performance was reflected in a series of analyst actions throughout the day. Citigroup upgraded FormFactor to Buy from Neutral, while B. Riley raised its price target to $66 from $52, and Stifel increased its target to $42 from $35. However, not all analysts were equally bullish, with TD Cowen maintaining a Hold rating and Evercore ISI Group keeping an In-Line stance.

The after-hours plunge, despite the seemingly positive backdrop, could be attributed to profit-taking following the significant intraday gains. Alternatively, investors might be reacting to elements of the company's forward guidance or other factors not explicitly covered in the available news. FormFactor also announced its participation in the upcoming 2025 Midwest 1x1 Conference on November 6, which could provide more clarity on the company's outlook. As the market digests this mixed set of signals, investors will be keenly watching for any additional information that could explain the stock's volatile movement.