* Chip stocks tumble ahead of Nvidia's quarterly report
* Roku soars after strong forecast, quarterly results
* Tech stocks lead decliners on the S&P 500
* Indexes down: Dow 0.52 pct, S&P 0.53 pct, Nasdaq 0.78 pct (Updates to mid-afternoon)
Nov 9 (Reuters) - Wall Street dropped on Thursday, weighed down by losses in Apple and other technology stocks as investors turned their attention to a U.S. Senate Republican plan that could delay corporate tax rate cuts expected by investors.
The S&P 500 has risen about 21 percent since the election of President Donald Trump a year ago, fueled by his promises to cut corporate taxes and other business-friendly measures.
The Senate on Thursday was expected to unveil a tax cut bill that differs significantly from one detailed last week in the House, complicating matters for the Trump administration.
Bill Cassidy, a member of the Senate Finance Committee, said the Senate tax proposal would delay a corporate tax cut by a year to 2019, while Senator John Cornyn said Senate Republicans were looking to avoid such a delay.
"It's been a year since the election. We've gone up 22 percent on hopes of what the Trump agenda would bring, and while they're trying to work toward this thing, they haven't really accomplished much yet," said Michael O'Rourke, chief market strategist at JonesTrading in Greenwich, Connecticut.
"If progress is not made, the equity market should either pause or correct until meaningful progress is made."
At 2:20 pm ET (1920 GMT), the Dow Jones Industrial Average was down 0.52 percent at 23,441.42, while the S&P 500 had lost 0.53 percent to 2,580.73.
The Nasdaq Composite dropped 0.78 percent to 6,735.91.
The Philadelphia Semiconductor index, a top performer in 2017, slumped 2.25 percent ahead of a quarterly report by Nvidia, which fell 2.79 percent.
Seven of the 11 major S&P 500 sectors fell, with the technology index's 1.31 percent loss leading the decliners.
Apple, Microsoft, Alphabet, Oracle and Facebook weighed more on the S&P 500 than any other companies.
Technology has been the best performing S&P 500 sector so far this year with a 37 percent rise, despite concerns of stretched valuations.
Roku soared 49 percent after the video streaming device maker's quarterly results and guidance beat expectations.
Macy's jumped 13.89 percent after the department store operator's profit came in above expectations.
Dish Network rose 3.8 percent after the satellite and internet TV provider added subscribers in the United States in the third quarter and reduced the rate at which it lost existing customers.
Declining issues outnumbered advancing ones on the NYSE by a 1.89-to-1 ratio; on Nasdaq, a 1.71-to-1 ratio favored decliners. (Additional reporting by Tanya Agrawal and Caroline Valetkevitch; Editing by James Dalgleish)