Shares of Amazon, Facebook and Google-parent Alphabet climbed more than one percent.

Retailers, meanwhile, suffered a blow after Abercrombie & Fitch called off talks related to its possible acquisition after receiving inquiries from possible suitors.

Abercrombie plummeted 21.2 percent. Wal-Mart Stores and Nordstrom each tumbled 2.8 percent, while Gap lost 6.3.

Another retailer, Best Buy, dived 6.3 percent following reports that Amazon plans to launch its own service of technical experts to make house calls, in direct competition with Best Buy's "Geek Squad."

The Dow Jones Industrial Average shed less than 0.1 percent to 21,408.52.

The broad-based S&P 500 added 0.1 percent at 2,427.43, while the tech-rich Nasdaq Composite Index advanced 0.4 percent to 6,176.39.

Key events later this week include the appearance by Yellen, who will update lawmakers on the outlook for the US economy and her expectations for additional interest rate increases in her twice-annual appearance before congressional committees.

Earnings season gets underway in earnest on Friday with reports from JPMorgan Chase and other large banks. Banks are flush with cash after clearing the Federal Reserve stress tests, raising the prospect that financial giants could turn to acquisitions as a way to grow.