Amkor Technology and ASE Technology Holding sit at a physical chokepoint in the AI chip supply chain: they bond stacks of high-bandwidth memory (HBM) to logic processors and test the finished package before it ships to Nvidia, AMD or a hyperscaler's custom-chip designer. Both stocks fell sharply over the past month, but neither drop originated in a weakening AI business. Amkor's AI-exposed segment posted record revenue and ASE's core packaging-and-test unit had its best quarter on record. The declines instead trace to a smartphone-driven guidance miss at Amkor and a sector-wide chip selloff that swept up ASE despite its own strong results.

Amkor: a legacy miss overshadows an AI beat. Amkor, which packages and tests chips for customers including Apple and Nvidia and is building a new advanced-packaging plant in Peoria, Arizona, reported second-quarter revenue of $1.9 billion, beating estimates, with earnings per share of $0.70 against a $0.47 consensus. Its Computing segment — the AI/data-center piece — grew 20% sequentially to a record and was guided up roughly 30% more in the third quarter, driven by a data-center CPU packaging ramp. But Amkor's largest segment, Communications (smartphone and memory-linked assembly), grew just 6% sequentially and was guided down high-single-digits for the third quarter on declining Android unit volumes and memory supply constraints. Because that segment still dominates the revenue base, third-quarter total-revenue guidance of $1.95-2.05 billion missed the $2.11 billion analysts expected, and the stock fell 24% in a single session even though gross-margin guidance (18.5-19.5%) and EPS guidance ($0.72-$0.82) both beat consensus. Amkor also disclosed a 10-year advanced-packaging agreement with TSMC and a multi-year Nvidia partnership, with its Arizona Phase 1 capacity fully committed and a second Korea facility on track for year-end.

ASE: a record quarter, sold off by sympathy. ASE, the largest outsourced assembly-and-test house outside TSMC and the primary second source hyperscalers use for custom AI chip packaging, reported second-quarter revenue up 34% year-over-year. Its assembly-test-materials segment — 66% of revenue and 94% of operating profit — hit a record TWD 126.1 billion, up 36% year-over-year, with gross margin up 5.4 points and operating margin up 6.2 points. Its leading-edge advanced-packaging line is tracking a few hundred million dollars above its own $3.5 billion full-year target, and management raised 2026 capital spending by $2 billion, directing 70% of new equipment spending toward advanced capacity now running at 80-85% utilization — management called the pricing environment "very friendly." None of that stopped the stock from falling 6.6% on July 24 amid a broader "chip risk reset" with no ASE-specific news attached, part of a week in which chip stocks lost more than $1 trillion in market value on reports that memory maker SK Hynix was slowing HBM capacity expansion and on growing skepticism about AI-infrastructure spending returns.

Fundamentals: CONTRADICTS the selloff, valuation INCONCLUSIVE. For both companies, the businesses that explain this story — Amkor's Computing segment, ASE's leading-edge packaging line — accelerated in the same quarter the stocks fell, which contradicts a reading of the drop as fundamentally driven. Amkor now trades at 22.3x forward earnings, below its own trailing 24.7x and below the 25-30x forward range the desk's own notes flagged for it in May, with EV/EBITDA of 10.6x — cheaper against its recent history after the drawdown, not more expensive. ASE's trailing P/E of 42x looks rich against Amkor, but its own forward multiple data was internally inconsistent in this dataset and is not used here; the business case rests instead on 36% segment growth and expanding margins funded by negative free cash flow during a capex buildout that won't ease until 2027. Independent of either earnings report, TrendForce reported August 5 that TSMC is actively expanding outsourcing of its CoWoS advanced-packaging front-end step to outside assembly houses amid rising Nvidia and custom-chip demand — confirming, after the selloff, that the capacity-overflow dynamic underlying both stocks' AI thesis is still operating.

Technicals. Amkor's crash was a single violent session (July 28, -24%, bottoming near $42.73 on July 29 before recovering to about $55), not a gradual grind; ASE's decline was smaller and smoother, consistent with sector sympathy rather than a company-specific shock, and both had round-tripped roughly a third of the peak-to-trough loss by early August.

The setup

Where it stands — Both stocks are down roughly 20-35% from June/July highs after each posted record AI-segment growth in the same quarter they sold off. Would confirm — Amkor's Communications segment stabilizes or its Computing segment share of revenue keeps rising toward 2027, offsetting the phone-cycle drag. Would invalidate — Amkor's Q4 2026/H1 2027 guidance shows Communications weakness persisting without Computing-segment revenue large enough to offset it. Watch next — Amkor's Q3 2026 print (guided $1.95-2.05B revenue) and ASE's follow-through on its raised $10.5B 2026 capex plan. Valuation — Amkor 22.3x forward vs 24.7x trailing (below its own recent 25-30x anchor); ASE 42.1x trailing, forward multiple data unreliable in this dataset.