U.S. equities closed slightly higher on Monday as Wall Street looked ahead to a key speech from President Donald Trump.

"For the speech tomorrow night, people are looking to maybe hear more details" about policies, said Randy Warren, chief investment officer at Warren Financial. "He's delivered on most of his campaign promises. Now it's time for him to deliver on the tough ones."

Trump is set to speak at a joint Congress session on Tuesday, and investors will look for clues about the administration's plans for tax reform and deregulation.

"What I'm watching out for is whether his focus is on the pro-growth policies or on the populist message," said Dan Miller, director of equities at GW&K Investment Management.

The Dow Jones industrial average gained about 15 points, hitting a new all-time intraday high, with Boeing and Goldman Sachs contributing the most gains. The index also closed at a record high for a 12th straight session, its longest streak since 1987.

"People are going to be cautious because the market has run up on expectations of tax cuts and deregulation," said Peter Cardillo, chief market economist at First Standard Financial. "I think we'll see a bit of a repeat of last week."

The S&P 500 also hit all-time intraday and closing highs, rising 0.1 percent, with energy rising 0.8 percent to offset losses in telecoms. The Nasdaq composite gained 0.28 percent.

The major stock indexes recorded fresh record highs last week but did not post gains as strong as the week before.

"We have transitioned from an interest-rates driven bull market to an earnings-driven bull market. That's the main story," said Jeffrey Saut, chief investment strategist at Raymond James. "I think we've got another six, seven or eight years in this bull market. If you run the models ... you could see 4,000 on the S&P."