Nvidia's Surge Hides Broader Market Weakness

Nvidia Corp. (NASDAQ:NVDA) is approaching a $6 trillion valuation as major indexes hit record highs, but Rosenberg Research founder David Rosenberg warns that this strength is masking broader market struggles. Speaking on CNBC, Rosenberg highlighted weak market breadth, a metric that tracks how widely gains are distributed among stocks. He noted that this indicator often precedes broader market trends, saying, "Breadth, with a lag, ultimately leads what’s going to happen with prices."

Rosenberg pointed out that the average S&P 500 stock entered the week about 20% below its 52-week high, while the median stock was down 17%. He emphasized that the market has become increasingly concentrated in a few AI-linked companies, citing legendary strategist Bob Farrell’s observation that healthy markets require broad participation. "If you’re that bullish on AI, just focus on the hyperscalers, focus on the semiconductors," Rosenberg advised. "The rest of the stock market is not really behaving that well."

The gap between the cap-weighted S&P 500 and its equal-weight version widened sharply in September, with the former gaining 0.2% while the latter fell 4.4%. Nvidia now carries more index weight than the smallest 256 S&P 500 companies combined. Rosenberg suggested that the AI trade could falter when investors start questioning whether future revenues justify current spending. He compared the situation to the Nasdaq’s peak in March 2000, noting that the exact trigger for a market downturn is often unclear in hindsight.

Polymarket traders currently place about a 6% chance on an AI industry downturn by December 31, 2026. The contract defines a downturn as at least three stress events within 90 days, including Nvidia closing 50% below its all-time high and the iShares Semiconductor ETF (NASDAQ:SOXX) falling 40%. Rosenberg warned that weaker company guidance could be the signal that begins shifting market sentiment.