MKS Instruments' stock experienced a significant 24-hour plunge of 8.66% during post-market trading sessions. The sharp decline followed the company's release of its fourth-quarter financial results, which revealed a key profitability metric falling short of analyst expectations.

The primary driver behind the sell-off was MKS Instruments reporting an adjusted earnings per share of $1.58 for the fourth quarter, which substantially missed the IBES estimate of $2.45. This earnings disappointment overshadowed the company's revenue beat, with Q4 sales reaching $1,033 million compared to the estimated $1,022 million.

Investors reacted negatively to the lower-than-expected profitability, leading to the sharp price drop as the market digested the mixed quarterly performance. The company's forward guidance for the first quarter of 2026 also contributed to the market's assessment of its near-term prospects.