InvestNot yet confirmed elsewhere1 publisher2 min readPublished
Korean retail and foreigners took opposite sides of Samsung and SK hynix in after-hours trading
Retail investors net bought 139.83 billion won of Samsung Electronics in the Korea Exchange's 8 p.m. session while foreigners sold 133.60 billion won. Retail supplied 89.4% of turnover against 7.9% for foreigners, so the foreign side of the split is thin.
The Investor · Invest desk
Bar chart of net trades in billion won on the Korea Exchange's after-hours market. Retail investors net bought 139.83 of Samsung Electronics and net sold 92.14 of SK hynix. Foreign investors net sold 133.60 of Samsung Electronics and net bought 101.54 of SK hynix.
Net trade value, Korea Exchange after-hours market In billion won
| Item | Value | Claim |
|---|---|---|
| Retail net bought Samsung Elec. | 139.83 billion won | 16 |
| Foreigners net sold Samsung Elec. | 133.6 billion won | 17 |
| Retail net sold SK hynix | 92.14 billion won | 3 |
| Foreigners net bought SK hynix | 101.54 billion won | 4 |
What happened
- Foreign investors net bought 101.54 billion won of SK hynix, the stock retail investors sold most at 92.14 billion won, over the 16 sessions from Sept. 14 to Oct. 8.
- Nextrade, the alternative trading system, averaged 1.7008 trillion won a day in after-hours turnover, and the Exchange's evening session ran at about 74% of that.
- Thin order books triggered volatility interruptions 1,112 times on opening day and 426 times on Oct. 8, as a handful of orders moved prices.
Why it matters
- constraint The tape covers the Korea Exchange only, and on KOSPI-listed stocks that venue trades about 51% of what Nextrade does (771.2 billion won a day against 1.5129 trillion), so the pairing may look different where most of the volume sits.
- exposure The Exchange leads on the KOSDAQ board, where it trades 2.63 times Nextrade's volume (493.3 billion won against 187.9 billion), so the blue-chip flow behind the Samsung and SK hynix story is in the segment where it trails.
- cost Surveillance is a fixed cost: the nine-member task force is committed through year-end for a session that trades about 4.78% of daytime volume, whatever evening turnover does.
The split looks sharper in the ranking tables than it does against turnover. The tables are Korea Exchange and Koscom data as reported by en.sedaily.com. Foreigners' 7.9% share [8] of an average evening of 1.2645 trillion won [7] is about 99.9 billion won a day [18] (assuming the share is counted on the same basis as the net figures). On that basis their net purchase of SK hynix over 16 sessions equals about 1.02 days of their own average trading [19]. Retail's side is small in the same way: 89.4% of turnover [8] over 16 sessions [1] comes to roughly 18.09 trillion won [20], and the 139.83 billion won Samsung net purchase is 0.77% of it [21].
The pairs also match in size. Foreign selling of Samsung was 95.5% of retail's Samsung buying [22], foreign buying of SK hynix was 1.10 times retail's selling of it [23], and in Samsung Electro-Mechanics retail sold 31.53 billion won [14] while foreigners bought 33.01 billion [15]. Net positions in a stock must sum to zero across all holders, and institutions net sold only 15.71 billion won of Samsung Electronics [13], so foreigners took most of the other side of the retail purchase. In our view that makes the split a counterparty effect: retail trades mostly with itself, and foreigners absorb the imbalance left over.
The same totals fit other readings. Retail and foreigners each ranked Samsung and SK hynix as their top two net sales in the regular session over the same weeks [6], so each group bought in the evening one of the two stocks it was selling in the day: retail bought Samsung, foreigners bought SK hynix. If the evening is where daytime sellers reverse part of a sale, the pairing is a timing effect. Or a few heavy days could dominate the 16 sessions; the report does not break them out or explain the divergence.
We think the counterparty reading fits best. Matched sizes are what it predicts, and two unrelated round trips would be unlikely to land within about 5% of each other on Samsung [22] and 10% on SK hynix [23]. It fails in two cases. If foreigners' share of turnover rises while the signs stay put, the split is a preference. If the signs flip while the shares hold, the first month was noise.
What to watch
- Second-month Korea Exchange and Koscom flow data: whether retail keeps buying Samsung and foreigners SK hynix with foreigners' share of turnover roughly unchanged.
- A Nextrade investor-type breakdown for the same sessions, to test the pairing on the venue that trades more KOSPI stocks.
- The daily volatility-interruption count after the Oct. 8 reading, and any enforcement action from the surveillance task force.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence62
- Adoption5
- Hype gap+15
- Incentives
- Insufficient
- Confidence58
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Over the 16 trading days from Sept. 14, when the Korea Exchange's after-hours session debuted, through Oct. 8, retail investors' largest net purchase on the after-hours market was Samsung Electronics preferred shares at 72.3 billion won.
- [2]
Over the same period retail investors net bought 67.53 billion won of Samsung Electronics common shares on the Korea Exchange after-hours market.
- [3]
The stock retail investors sold most on the after-hours market was SK hynix, with net selling of 92.14 billion won.
- [4]
Foreign investors net bought 101.54 billion won of SK hynix on the Korea Exchange's after-hours market.
- [5]
Foreign investors net sold 83.11 billion won of Samsung Electronics preferred shares and 50.49 billion won of Samsung Electronics common shares on the after-hours market.
- [6]
In the regular session over the same period, both retail and foreign investors ranked Samsung Electronics and SK hynix as their top two net sales.
- [7]
Average daily turnover on the Korea Exchange's after-hours market was 1.2645 trillion won, about 4.78% of the regular session.
- [8]
Retail investors accounted for 89.4% of total turnover on the Korea Exchange's after-hours market, compared with 7.9% for foreign investors and 1.6% for institutions.
- [9]
Average daily turnover on the after-hours market run by Nextrade (NXT), the alternative trading system, was 1.7008 trillion won; the Korea Exchange's average is roughly 74% of that.
- [10]
For KOSPI-listed stocks, average daily after-hours turnover at NXT (1.5129 trillion won) far outpaced the Korea Exchange (771.2 billion won); for KOSDAQ stocks the Korea Exchange (493.3 billion won) was more than 2.5 times NXT (187.9 billion won).
- [11]
With thin order books, 1,112 volatility interruption triggers were recorded on the session's opening day; the figure fell to 426 on Oct. 8.
- [12]
The Korea Exchange is running a nine-member special surveillance task force for the after-hours market through the end of the year to block unfair trading.
- [13]
Institutions net sold 15.71 billion won of Samsung Electronics on the after-hours market.
- [14]
Retail investors net sold 31.53 billion won of Samsung Electro-Mechanics on the after-hours market.
- [15]
Foreign investors made Samsung Electro-Mechanics their second-largest net purchase at 33.01 billion won.
- [16]
Retail net purchases of Samsung Electronics preferred and common shares total 139.83 billion won.
- [17]
Foreign net sales of Samsung Electronics preferred and common shares total 133.60 billion won.
- [18]
Foreign investors' average daily after-hours turnover on the Korea Exchange is about 99.9 billion won, assuming the share is measured on the same basis as the net figures.
- [19]
Foreigners' 101.54 billion won net purchase of SK hynix equals about 1.02 days of their average daily turnover.
- [20]
Retail turnover over the 16 sessions is roughly 18.09 trillion won.
- [21]
Retail's 139.83 billion won Samsung net purchase is about 0.77% of its 16-session turnover.
- [22]
Foreign net selling of Samsung Electronics was 95.5% of retail net buying of it.
- [23]
Foreign net buying of SK hynix was 1.10 times retail net selling of it.
- [24]
On KOSPI-listed stocks the Korea Exchange's after-hours turnover is about 51% of NXT's.
- [25]
On KOSDAQ stocks the Korea Exchange's after-hours turnover is about 2.63 times NXT's.
- [26]
The source attributes the KOSDAQ gap to NXT's after-hours market being centered on blue chips, while the Korea Exchange allows trading in effectively all listed stocks, including KOSDAQ.
Sources
1 independent publisher whose own reporting we read for this story.
- en.sedaily.comRetail Investors Buy Samsung, Dump SK hynix in Exchange After-Hours Debut
1 article · October 11, 2026
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