Tech stocks saw $8.5 billion of inflows in the week, BoFa said, citing market data provider EPFR. Stocks in general saw $14.8 billion of inflows, the largest weekly inflow since February.

The Nasdaq and S&P 500 hit nine-month closing highs on Thursday.

Part of that upsurge was thanks to a 30% rise in shares of chipmaker Nvidia in just three sessions that pushed its market valuation above $1 trillion at one point.

Investors are chasing a "summer rip tide into tech and stocks," BofA analysts wrote in a note, which referred to an AI "baby bubble," though they said they themselves remain bearish due to the impact of higher interest rates causing liquidity to tighten.

They said the market is "bored of waiting for rates to cause recession" and so is moving back into the biggest companies which had the biggest margins and biggest price to earnings multiples.

Seven stocks - Apple, Microsoft, Google parent Alphabet, Amazon, Nvidia, Meta and Tesla - account for 8.8 percentage points of the S&P 500's 10% year-to-date return, according to BofA's calculations.

This is making some investors nervous, as a rally driven by a handful of stocks raises questions about the health of the broader market and risks igniting volatility if investors ditch those megacap holdings.

Cash funds, normally in demand when investors are nervous, also saw inflows of $11.3 billion, their sixth straight week of inflows, while gold funds saw $200 million of outflows, according to BofA.

BofA suggested a contrarian trade of buying Hong Kong's Hang Seng Tech Index, which includes many big Chinese tech names, and selling the Nasdaq 100, on hopes for a surprise stimulus from China this month.

They describe the trade as: "Buy HSI sell AI."