The S&P 500's performance is increasingly influenced by a select group of mega-cap technology stocks, particularly those benefiting from the intense investor focus on artificial intelligence. This trend was evident on Thursday, when AI chip designer Nvidia's shares surged 8.7% following its second-quarter earnings, adding a record $441.5 billion to its market value, which reached $5.49 trillion. As Nvidia holds a significant weighting in the S&P 500, its rally propelled the index higher, despite the average stock underperforming.