Recently, an email from within tech giant Microsoft (MSFT -0.80%) may have confirmed investors' fears: AI spending has become excessive. High spending on AI is a key reason investors have expressed concerns about tech stocks like Microsoft, fearing the investments won't pay off. Expand NASDAQ : MSFT Microsoft Today's Change ( -0.80 %) $ -4.03 Current Price $ 502.03 Key Data Points Market Cap $3.8T Market cap calculated using publicly traded shares outstanding only. The danger is that history could repeat itself, and highly valued tech stocks may fall sharply in value. But for other tech stocks, investors should be careful and pay close attention to their valuations, as buying at inflated levels could be risky.