Gidongju (Momentum Stock)

A stock whose trading volume and share price move sharply in a short period, meaning a stock whose volatility widens due to themes, news, and supply-demand dynamics.

Gidongju (Momentum Stock)

Overview

Gidongju (起動株) refers to stocks whose share price and trading volume move sharply in a short period in response to a specific catalyst or theme, news, or changes in supply and demand. They generally have small market capitalizations and few floating shares, so even a small amount of capital can make the price swing widely, and among investors the term is used interchangeably with "surge stocks," "theme stocks," and "junk stocks." However, because gidongju rise and fall quickly alike, they are classified as a very high-risk asset class with substantial volatility risk.

Key Content

Definition and Concept

Gidongju is a practitioner's term that began with the meaning "a stock whose price has begun to move," and it is not a classification with a clear academic definition. In the securities industry, a stock is usually regarded as a gidongju when it shows trading volume 3–5 times or more its daily average together with a price change of 10% or more in a short period (one day to several weeks). In other words, the key lies in the phase in which supply-demand and sentiment, rather than fundamentals, determine the price.

Causes

1. Themes and catalysts: When expectations form for a particular industry—government policy, new technology, overseas issues, and the like—related stocks surge together.

2. Concentrated supply and demand: When large buying by foreign and institutional investors, program trading, and short covering overlap, prices change abruptly.

3. Lack of floating shares: For small-cap, low-liquidity stocks, even a small amount of buying pressure can push the price to the daily limit.

4. Disclosures and news: Earnings surprises, mergers and acquisitions (M&A), new product launches, clinical results, and similar events serve as catalysts.

5. Herd psychology: When a stock becomes a hot topic in communities and on social media, retail investors' chase buying flows in and the rally accelerates.

Characteristics

High volatility: Daily moves of 20–30% are common, and prices may repeatedly hit the upper and lower limits.
Short lifespan: Most gidongju show a "retracement," returning to their original price within days to weeks as the catalyst fades.
Volume surge: They are accompanied by trading volume dozens of times the usual level, and turnover is very high.
Information asymmetry: The truth of the catalyst is often unclear, making "rumor trading" likely.

Precautions When Investing

It is no exaggeration to say that trading gidongju is all about timing. If entry is late, there is a large risk of being "stuck at the top," and conversely, there are many cases in which losses widen while waiting for a rebound in a downtrend. Therefore, ① setting stop-loss rules, ② diversifying investments, ③ checking volume and supply-demand data, and ④ judging the persistence of the catalyst are essential. In addition, since there are cases of artificial surges caused by market makers or manipulation rings, one must be wary of spoofing orders or abnormal surge patterns.

Related Regulations

To curb overheating caused by gidongju, the Korea Exchange operates systems including price limits (±30%), suspension of trading, designation as short-term overheating stocks, and designation as investment warning/risk stocks. Since 2023, with the introduction of the alternative trading system (Nextrade), volatility interruption (VI) mechanisms have been reorganized several times.

Latest Trends

In 2024–2025, the gidongju market is showing the following changes.

Repeated rotation of AI, semiconductor, and secondary battery themes: With each earnings season for global AI companies such as Nvidia, related component and equipment stocks emerge as gidongju.
Growing share of retail investors: Individual capital—dubbed "Seohak Gaemi" and "Donghak Gaemi"—moves quickly into theme stocks, tending to amplify volatility.
Impact of algorithmic and high-frequency trading (HFT): As ultra-short-term trading increases, intraday price swings widen and the speed of reaction to news has accelerated.
Tighter regulation: Financial authorities continue to pursue investigations into unfair trading of abnormally surging stocks and improvements to the short-selling system.
Global synchronization: Cases are increasing in which the meme stock trend on the U.S. Nasdaq spills over into domestic theme stocks.