U.S. stocks open higher amid Yellen's testimony

U.S. stocks opened higher Wednesday as Wall Street eyed U.S. Federal Reserve Chair Janet Yellen's semi-annual testimony.

Yellen will continue her testimony for a second day with a session scheduled later Wednesday morning before the House Financial Services Committee.

In her testimony Tuesday before the Senate Banking Committee, Yellen reiterated the U.S. central bank's intention to raise interest rates, taking a cautious approach in view of an uncertain U.S. economy.

She pointed out "considerable uncertainty" about the U.S. economic outlook, which includes slow job gains, weak investment, slow productivity growth, and vulnerabilities in the global economy.

She said that the central bank expected interest rates to remain low for some time, in view of the weak global economy and sluggish productivity growth.

Investors were also counting down the hours to Britain's referendum, which is scheduled to begin Thursday morning.

Shortly after the opening bell, the Dow Jones Industrial Average rose 24.38 points, or 0.14 percent, to 17,854.11. The S&P 500 added 3.53 points, or 0.17 percent, to 2,092.43. The Nasdaq Composite Index went up 5.01 points, or 0.10 percent, to 4,848.77. Endi