The primary objective of this study was to examine the impact of the US sovereign credit rating downgrade on its equity market. Utilizing the event study methodology, a sample of three most capitalized listed companies -- Microsoft, Apple, and Amazon -- and the equity market index -- S&P500 -- were used as the proxy for the overall equity market. Three market models were constructed within the estimation window to determine the expected daily returns on the selected companies stocks. The result showed that the sovereign credit rating downgrade of the US government debt did not have any significant effects on the US equity market.