Memory chip stocks are experiencing a significant sell-off in the pre-market session, continuing a trend from Asian markets. The decline is driven by investor concerns over stretched valuations in the AI sector and questions about the sustainability of the recent massive spending on AI infrastructure. This profit-taking follows a period of exceptionally strong performance, and even positive news, such as a record profit for TSMC, has not stemmed the decline as focus shifts to high capital expenditures and potential margin pressures.