What an alternative trading system is
An alternative trading system is a venue that matches stock trades separately from the established stock exchange. It does not list new companies; it only matches buy and sell orders in a selection of stocks that are already listed. The US has long had many exchanges and off-exchange venues operating side by side, but in Korea a single exchange handled stock trading for a long time. When Korea's first alternative trading system began trading in March 2025, the same stock started trading on two venues at once.
What has changed
From an investor's point of view, the visible changes come down to a few points. Details can change, so check the official information from the exchanges and your broker as well.
- The time during which Korean stocks can be traded has been extended before and after the regular session
- The same stock trades on two venues, so prices can differ slightly for a moment
- Brokers split orders and send them to whichever venue offers better terms
- Only some listed stocks, not all of them, trade on the alternative venue
Longer hours and the character of the chart
The sessions before and after regular hours behave much like US pre-market and after-hours trading. There are fewer participants than during the regular session, so volume is thin, and small orders can make the price jump or the bid-ask spread widen. At the same time, these sessions become a window in which the overnight US session, or filings and news released after the close, are reflected in prices before the regular session opens. For example, if US chip stocks moved sharply overnight, the reaction may show up first in pre-session trading of Samsung Electronics and SK Hynix. There is no guarantee, however, that the pre-session price becomes the regular session's opening price.
Where chart data starts to differ
With two venues running together, the same stock can show slightly different candles on different chart screens. Checking these points first explains most of the differences.
- Whether the chart includes only the main exchange's trades or combines both venues
- Whether pre- and post-session trading is included in intraday and daily candles
- Which venue and which moment's price define the daily open and close
- Whether volume is for one venue or the combined total
Reading the open, close and volume
In chart analysis, the open, the close and volume are the most basic values. On a chart that includes pre- and post-session trading, the body and wicks of a daily candle can look different from a chart that shows only the regular session, and a high or low set in pre-session trading can remain as a wick on the daily candle. Volume is also split across two venues, so looking only at one venue's volume can make it seem smaller than it really is. When volume seems to drop suddenly, first work out whether interest has cooled or trades have simply moved to the other venue.
Common mistakes
Until you get used to the new setup, these misreadings come up often. Most of them come from not checking what basis the chart in front of you was drawn on, so it helps to make a habit of looking at the session and venue settings in the chart options first.
- Reading the pre-session price as the direction of that day's regular session
- Concluding that trading has dried up from one screen's volume alone
- Assuming every stock trades during the extended hours
- Comparing the same day's candle across charts built on different bases
Check it with this site's live tools
The world markets overview shows major indexes, including the KOSPI, and which markets are open right now on one screen, and the Korea and US large-cap scanner shows daily moves, volume and moving average alignment for Korean large caps such as Samsung Electronics and SK Hynix alongside US large caps. The Korean quotes in these tools come from an outside data provider, so they may not include trades on the alternative venue or in the pre- and post-session hours. The world clock shows the time difference between New York and Seoul. Prices may be delayed.
Things to keep in mind
This guide explains how Korea's alternative trading system and longer trading hours affect charts; it is educational material, not investment advice. The stocks mentioned are examples of chart reading only, not suggestions to buy or sell. Details that can change, such as trading hours, eligible stocks, fees and order types, are deliberately left without numbers, so be sure to check the official information from the exchanges and your broker. Remember too that pre- and post-session trading is thin, so orders may not fill at the price you want.
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