(Reuters) - U.S. stocks climbed to record highs on Monday, helped by optimism about merger activity and as investors bet that a Republican plan to cut corporate taxes would bolster earnings.

Qualcomm QCOM.O rose 1.15 percent after Broadcom AVGO.O offered to buy the smartphone chip supplier for $103 billion in what could be the biggest-ever acquisition in the tech sector. Broadcom added 1.42 percent.

“The fact that the deal is on the table is huge,” said Paul Nolte, portfolio manager at Kingsview Asset Management in Chicago.

“We have not seen much in the way of dealmaking this year. So this might jump-start some of the dealmaking ahead of the tax policy changes.”

Twenty-First Century Fox FOXA.O surged 9.93 percent after CNBC reported that the film and television conglomerate has held talks to sell most of the company to media giant Walt Disney Co DIS.N. Disney shares rose 2.02 percent.

Investor optimism was also fueled by a Republican proposal last week to slash the corporate tax rate to 20 percent from 35 percent and end some tax breaks for companies and individuals.

“I think that has to be the main driver,” said John Brady, managing director at R.J. O’Brien & Associates in Chicago. “Even if it only goes to 25 percent or 27 percent, it’s still moving the right way.”

Apple AAPL.O rose 1.01 percent and contributed more than any other stock to the benchmark S&P 500 index's gain.

Shares of Sprint S.N slumped 11.54 percent to a more than one-year low after the wireless provider and T-Mobile TMUS.O called off a planned merger. T-Mobile lost 5.72 percent.

Traders work on the floor of the New York Stock Exchange (NYSE) in New York City, New York, U.S., October 27, 2017. REUTERS/Brendan McDermid

All three major indexes closed at record highs.

The Dow Jones Industrial Average .DJI inched up 0.04 percent to end at 23,548.42, while the S&P 500 .SPX gained 0.13 percent to 2,591.13.

The Nasdaq Composite .IXIC added 0.33 percent to 6,786.44.

The S&P 500 energy index .SPNY surged 2.2 percent on gains in crude prices LCOc1CLc1 after the crown prince of Saudi Arabia, the world's largest oil exporter, tightened his grip on power through an anti-corruption purge. [O/R]

In extended trade, Priceline Group PCLN.O lost 6 percent and Weight Watchers International WTW.N jumped 10 percent after those companies reported quarterly results.

With more than 400 of S&P 500 companies having reported, earnings for the third quarter are expected to have climbed 8 percent, compared with expectations of a 5.9 percent rise at the start of October, according to Thomson Reuters I/B/E/S.

Up 15 percent in 2017, the S&P 500 is trading at about 18 times expected earnings, according to Thomson Reuters Datastream.

Michael Kors KORS.N jumped 14.70 percent after the fashion accessories maker raised its 2017 revenue forecast. The stock was the biggest percentage gainer on the S&P.

Advanced Micro Devices AMD.O jumped 7.28 percent after a report that it plans to team up with Intel INTC.O to form a personal computer chip unit. Intel ended 1.37 percent higher.

Advancing issues outnumbered declining ones on the NYSE by a 1.41-to-1 ratio; on Nasdaq, a 1.17-to-1 ratio favored advancers.

About 6.6 billion shares changed hands on U.S. exchanges, above the 6.4 billion daily average over the last 20 sessions.