A retail investor surnamed Min knew the risks before pressing the buy button. But the urge to make up for the gains he had missed overwhelmed his better judgment. In early July, the 29-year-old purchased 5 million won ($3,496.26) worth of Direxion Daily Semiconductor Bull 3X Shares, an exchange-traded fund (ETF) known by its ticker, SOXL. The fund seeks to deliver three times the daily return of the Philadelphia Semiconductor Index. When he checked his account the next morning, his position was already down more than 10 percent. He saw the decline as another buying opportunity and added to his holdings. His losses continued to deepen, eventually reaching 30 percent. "I naively thought that the bad news surrounding chip stocks would end just after I bought in, followed by a sharp rebound," he said. "I let the fear of missing out take over." Min is one of many retail investors who have piled into triple-leveraged U.S. ETFs as chip stocks have languished at home and Korean authorities have tightened regulations on trading single-stock leveraged ETFs tied to Samsung Electronics and SK hynix.