Marvell Technology Group Ltd is trading 3.3% up at $299.20 in after-hours trading. - The significant gains follow news that Marvell will join the S&P 500 Index effective June 22, driving index-related buying. - The stock also benefited from a strong endorsement by Nvidia's CEO, who reportedly called Marvell the "next trillion-dollar company" amid bullish sentiment on its AI chip opportunities. - These company-specific catalysts, along with a broader rebound in AI and semiconductor stocks, fueled the rise despite major market indices ending lower on June 17, 2026.