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Amid the AI Boom, the Technology sector's weighting in the S&P 500 has now eclipsed 1/3rd of the index.  As shown in the first chart below, the only time the sector's weighting has been higher was during a brief window in early 2000 at the peak of the Dot Com bubble.

But the first chart only tells part of the story.  Back in 2018, those in charge of sector classifications reorganized many stocks in the S&P.  Already-big stocks like Alphabet (GOOGL) and Meta (META) -- Facebook at the time -- were shifted out of the Technology sector and into the newly classified Communication Services sector.  This resulted in a big drop in the Tech sector's weighting in September 2018 that you can see quite clearly in the chart.

In the second chart below, we've included a red line that shows where the Technology sector's weighting would be right now if the pre-2018 sector classifications were still in effect.  Tech would have a weighting in the S&P 500 of roughly 43% right now rather than 33.6% if pre-2018 classifications were in place.  43%!

While its sky-high weighting could be a warning sign, Tech remains the driving force for the US stock market, while every other sector plays second fiddle.
 

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