KOSPI Buy-Side Sidecar Triggered After 4.52% Surge, Program Trading Halt

South Korea’s KOSPI triggered a **buy-side sidecar** on **March 30, 2025**, after the index jumped **4.52%** to **5,281.04**. It was the **first buy-side activation in ~20 days**. The mechanism is a volatility curb that temporarily halts **program trading** to slow momentum-driven price acceleration. **When it triggers:** the **buy-side sidecar** activates if the KOSPI rises **more than 4% within a 5-minute window**. A **5-minute cooling-off period** then applies specifically to **program buy orders**, aiming to reduce algorithmic feedback loops. **Market impact:** during the cooling period, **order-book depth improved** as limit orders accumulated. After the pause, the index **held most gains**, closing **+4.52%**. Trading volume reached about **150%** of the 30-day average, and advancers outnumbered decliners by roughly **4:1**. Tech/semiconductors led, with **Samsung Electronics** and **SK Hynix** up **over 6%**, while autos also rose. **Regulatory and surveillance:** South Korea’s **FSC/FSS** reviewed the event to ensure disorderly trading was contained and price discovery remained fair. Market surveillance flagged unusual patterns, and KRX maintained full audit trails. For traders, the key takeaway is that the **buy-side sidecar** can abruptly change liquidity and short-term momentum dynamics—often without signaling a fundamental trend break.