London — Outsized returns for memory-related stocks have helped fuel substantial gains in U.S. and South Korean equity markets in recent years — but market watchers warn investors forget the market's cyclicality at their own risk. The memory industry has been in a period of sustained growth since the launch of ChatGPT in December 2022, which triggered huge demand for high-bandwidth memory, or HBM. Samsung and SK Hynix are among the largest producers of HBM chips, and their stock prices have