KOSPI Weekly Market Review for the 5th Week of October — From a +6.63% surge on the 28th to a -3.48% plunge on the 30th, a rollercoaster week

During the week of October 26–30, 2026, the KOSPI gained 3.25%, while the KOSDAQ tumbled 3.63%. The main index spiked 6.63% in a single session on October 28 to reclaim the 6,000-point mark for the first time in 10 trading days, before pulling back 3.48% on October 30 to close at 5,730.74. Here is a breakdown of what drove this high-volatility week, backed by market headlines and our internal data.

1. Weekly Closing Summary for the 4 Major Indices

The KOSPI logged daily returns of -1.46%, +3.09%, +6.63%, -1.24%, and -3.48%. The KOSDAQ posted -3.26%, +2.29%, +3.69%, -2.34%, and -3.83%, meaning late-week losses completely wiped out the early-week bounce. Note that U.S. index returns reflect their regular session closes through October 30 (KST), where the Nasdaq 100 plunged 3.46% and the S&P 500 dropped 1.82% on Friday.

2. What Sparked the Big Rally on October 28?

On October 28, the KOSPI closed at 6,012.44, regaining the 6,000 level for the first time in 10 sessions. Financial media highlighted the following catalysts:

• SK Hynix Shareholder Return Plan: SK Hynix unveiled a fresh dividend and share buyback strategy, sending its shares skyrocketing 10.89% (News1, Gyeongbuk Maeil). Samsung Electronics also surged over 9%.
• Anthropic IPO Rumors: News broke in the U.S. that AI startup Anthropic was prepping for an IPO, temporarily easing market jitters over the sustainability of AI capital spending (Asia Business Daily, Gyeongbuk Maeil).
• Foreign & Institutional Inflows: Both foreign funds and domestic institutions stepped in with heavy net buying (News1, Gyeongbuk Maeil), while retail investors took profits. Keep in mind that these are media narratives—a massive one-day rally is rarely caused by a single isolated event.

3. Why Did the Market Tank on October 30?

The Friday slump was triggered by disappointing earnings from Big Tech in the U.S. MTN reported that Alphabet's earnings fell short of expectations, reigniting concerns about the return on AI investments. Global Economic cited Shinhan Securities analysis pointing to Google's widening negative free cash flow and Amazon's mounting cash flow strain from escalating CapEx.

• The KOSPI plunged over 5% intraday (hitting a low of 5,599.42), and a sell-side circuit breaker ("sidecar") was triggered for KOSPI 200 futures around 10:05 AM.
• Mega-cap chipmakers took a direct hit: Samsung Electronics sank 3.02%, and SK Hynix plunged 7.08%.
• According to Global Economic, foreign investors dumped roughly 1.62 trillion KRW worth of KOSPI shares, while institutional (742.6 billion KRW) and retail investors (621.0 billion KRW) absorbed the selling.

Semiconductor giants that led Wednesday's rally swung violently back down just two days later as the AI profitability debate reignited.

4. What Our Data Revealed This Week

Sentiment: The KOSPI Fear & Greed Index crept up from 16.0 to 19.8, while the KOSDAQ Fear & Greed Index slid from 25.0 to 17.5. The KOSPI lingered in "Extreme Fear" (below 25) for 3 out of 5 sessions (Oct 26: 17.3, Oct 29: 22.9, Oct 30: 19.8), while the KOSDAQ spent 2 days there (Oct 26: 24.96, Oct 30: 17.5). During the October 28 rally, sentiment briefly recovered to 30.9 on the KOSPI and 39.5 on the KOSDAQ. In the U.S., both the S&P 500 (20.0 → 33.5) and Nasdaq 100 (12.7 → 26.2) climbed out of Extreme Fear into regular Fear territory.

Counting how many times all four indices dropped into Extreme Fear (crossing below 25 from above): we saw 6 instances during the week of October 19 (KOSPI: 2, KOSDAQ: 1, S&P 500: 2, Nasdaq 100: 1), 3 instances this week (KOSPI: 1, KOSDAQ: 2), and 2 the week prior. Sentiment score swings were unusually rapid this week, triggering short-lived entries and exits.

Note: On October 26, the KOSDAQ score was 24.96. While it rounds to 25.0, anything strictly below 25 is classified as Extreme Fear.

Sectors: We tracked the top 30 KOSPI sectors by market cap on our Sector Radar, comparing 5-day relative strength between October 23 and October 30.

Themes: On Theme Rankings, Semiconductors took the top spot in total trading value (41.70 trillion KRW), followed by Non-Memory Chips (41.43 trillion KRW) and System-on-Chip/Memory (40.99 trillion KRW). Last week's leader, Weak KRW Beneficiaries, dropped to 4th place (40.76 trillion KRW). (Excludes broad index themes; based on top 50 daily listings).

Top Gainers: We identified specific news catalysts for 150 surging stocks. Cybersecurity led all thematic groups with 12 breakout names (e.g., AhnLab +19.63% / +17.78%, RaonSecure +16.34%). News items cited headline hacks at crypto exchanges and financial firms, alongside AhnLab's strong Q3 earnings.

5. Historical Backtest: What Happens After Hitting "Extreme Fear"?

Using our KOSPI Fear & Greed Index historical tool, we backtested every instance where sentiment plunged into "Extreme Fear" (<25). Since February 13, 2025, there have been 21 initial entry signals. Here is how the KOSPI performed 1 week (5 days), 1 month (20 days), 3 months (60 days), and 6 months (120 days) after hitting that signal:

Fewer sample counts exist for longer horizons as recent signals have not yet matured. Across all cases, the worst drawdowns were -32.6% (1-month) and -18.1% (3-month), while the best 6-month gain reached +102.8%. Figures are price returns excluding dividends.

Keep three key caveats in mind:

1. These 21 signals are not independent events. If you cluster re-entries occurring within 20 trading days, they condense into just 5 distinct market events. One persistent pullback starting June 23, 2026 alone generated 9 separate entry signals.
2. The 6-month sample size is tiny (8 cases). As flagged on our tool interface, sample sizes under 10 carry low statistical reliability.
3. The backtest window coincided with a massive bull run, where KOSPI rallied from 2,328 (April 2025) to 8,204 (June 2026). Past performance under macro tailwinds will not necessarily repeat.

The current setup is already diverging from past averages. The current episode began on October 13 (now 13 trading days in), and the KOSPI was down 8.0% five days after the initial signal. In all four previous clusters, the index was actually up 5 days post-signal (+1.9% to +10.1%). The October 30 close of 5,730.74 stands 5.0% below the signal entry level (6,035), having hit a trough of 5,469.47 (-9.4%) on October 26. Historical backtests provide context, not a crystal ball. For maximum drawdown data and recovery speeds back to a score of 40, check out our previous post.

6. Institutional Filings to Note

• National Pension Service (NPS): Out of 8 filings submitted this week, the NPS reported a new 10.00% major stake in Samsung E&A as of October 28. Meanwhile, its stake in Hyundai E&C dipped below the 10% threshold, trimming down from 10.56% to 9.93% on October 30 (NPS Portfolio Changes).

What to Watch Next Week

The KOSPI spent only two days (Oct 27–28) above the 25-point threshold this week, while the KOSDAQ sat right on the edge. You can track whether sentiment holds above or below Extreme Fear on our KOSPI and KOSDAQ Fear & Greed dashboards. To see if dramatic sector rotations—like Construction collapsing from #1 to #27 and Autos dropping from #11 to #29—continue, monitor our live Sector Radar.

Media References: News1 (Oct 28 Close), Asia Business Daily, Gyeongbuk Maeil, MTN (Oct 30), Global Economic

Disclaimer: This post is for informational purposes only and does not constitute investment advice. Index values, sentiment scores, and rankings are aggregated by 10Bagger. Market commentary and net flow figures are sourced from the media reports cited above.