US stock futures fell sharply on Tuesday, pointing to a weak opening for Wall Street. Nasdaq 100 futures dropped 2.5%, S&P 500 futures fell 1.3%, and Dow Jones futures were down about 0.6%. The biggest pressure came from technology stocks. A global sell-off in tech shares spread from the United States to Asian markets, hurting investor confidence.US stock market today: S&P 500, Nasdaq and Dow Jones move as investors track tech stocks. (Photo by Michael M. Santiago / GETTY IMAGES NORTH AMERICA / Getty Images via AFP) (Getty Images via AFP)Investors became worried about the AI-driven stock market rally. Many traders are now questioning whether huge investments in artificial intelligence will generate enough profits to justify current stock prices, as noted by Moneycontrol. The weakness started after losses on Wall Street the previous day. The Nasdaq Composite had already fallen 1.3% overnight, while the S&P 500 also closed lower as investors sold major technology stocks.South Korea market crashA major shock came from South Korea's stock market. The Kospi Index crashed 10%, forcing a temporary halt in trading due to heavy selling pressure. Chipmakers were at the center of the sell-off. SK Hynix and Samsung Electronics shares plunged more than 12%. Reports about AI memory-chip production triggered investor fears. According to Moneycontrol, reports suggested that SK Hynix may slow the expansion of AI memory-chip production and focus more on traditional DRAM memory products.The news raised concerns about future AI demand. Technology stocks across Asia were hit hard. The Asian technology stock index fell as much as 5%. The decline ended a strong winning streak for Asian tech shares. The Asian tech index snapped an eight-session winning streak. The AI trade has been one of the biggest market themes of 2026. AI-related enthusiasm helped major global stock markets reach record highs this year.Micron earnings in focusTuesday's sell-off raised fresh doubts about those high valuations. Investors are becoming increasingly cautious about paying premium prices for AI-related companies. Market attention is now shifting to Micron Technology. The company's quarterly earnings report later this week is expected to provide important clues about AI memory-chip demand. Micron's results could influence the next move in technology stocks. Investors want updates on data-centre spending and overall AI infrastructure demand.Also read: Stock market today: Why are US stocks lower today? Tech selloff, Iran talks and PCE inflation data weigh on marketsStock valuation concernsConcerns about expensive stock valuations returned to the market. According to Moneycontrol, many investors believe some AI-linked stocks may have risen too far, too fast. SK Hynix had already seen an enormous rally before the crash. The stock had surged nearly 350% in 2026 before Tuesday's sharp decline. Signs of excessive speculation were also visible. Margin borrowing by South Korean retail investors recently reached a record high.High borrowing levels often increase market risks. Heavy use of borrowed money can make market declines more severe when investors rush to sell. The tech sell-off overshadowed positive geopolitical developments. Easing tensions involving Iran received little attention from investors. Oil prices actually moved lower during the market turmoil. Brent crude fell below $77 per barrel.Global markets turn weakA US policy decision helped reduce oil-market concerns. The United States reportedly issued a 60-day licence allowing Iran to continue selling oil internationally. The move was seen as support for ongoing US-Iran peace talks. The decision helped ease fears of supply disruptions in global oil markets.The selloff in the tech world also made waves in the European markets, as Stoxx Europe 600 Index fell 0.92% in early trading, dragging other indices lower as well as investors looking to buffer against the riskier bets. It was the culmination of the broader "risk-off" feeling, and encouraged traders to reduce exposure to growth-focused stocks.And as has been the case in most markets; including the S&P 500 and Nasdaq drops and the concern was that most major A.I. companies are having inflated valuations with little or no profits at hands. Add to it the South Korean market crash and weak sentiments among global chipmakers, as per Moneycontrol, which all led to global sell- offs.In simple terms, investors suddenly became worried that AI companies may not deliver enough profits to justify their massive stock market gains. That fear sparked selling in technology shares worldwide and pushed Wall Street futures sharply lower.