U.S. stocks open mostly higher as Nvidia drives tech rally

U.S. stock indexes opened mostly higher with the Nasdaq Composite
COMP,
+1.68%
soaring 1.7% after Nvidia Corp.
NVDA,
+27.27%
gave stronger-than-expected revenue guidance for its fiscal second quarter, pushing its shares toward all-time highs and propelling the company to the cusp of a $1 trillion market value. Wall Street is also betting on other semiconductor manufacturers with shares of Advanced Micro Devices
AMD,
+9.71%
jumping 9% and Monolithic Power Systems
MPWR,
+12.53%
up 14.2%. The Dow Jones Industrial Average
DJIA,
-0.13%
was off 55 points, or 0.2%, to 32,744, while the S&P 500
SPX,
+0.84%
advanced 0.7%. The top triple-A credit ratings of the U.S. were placed on “rating watch negative” by credit firm Fitch Ratings Wednesday evening, due to “brinkmanship” in Washington which increases the risk that the country could default on some of its debt and other obligations. In economic data, the number of Americans who applied for unemployment benefits before Memorial Day weekend totaled just 229,000 after Massachusetts took dramatic steps to weed out a massive increase in fraud.