A steep drop in technology stocks on Friday, led by Apple's worst plunge in 14 months, has left investors concerned that a rally may be over for high-flying Silicon Valley names that have pushed Wall Street to record highs this year.

The S&P 500 information technology index dropped 2.73 percent, with Apple, Amazon.com and Alphabet down more than 3 percent each and the Nasdaq Composite losing 1.8 percent.

The losses in just those three stocks wiped out more than $68 billion in investor wealth.

CNBC reported that the so-called "big five" — which would included Apple, Alphabet Class A shares, Microsoft, Facebook and Amazon — lost more than $97.5 billion in market value between the close on Thursday and the close on Friday, according to FactSet, dragging the Nasdaq to its worst week of the year.

"All you need is a spark. Everything has gotten pretty expensive, multiples are very high. It doesn't take much to get a decline started," said Stephen Massocca, senior vice president at Wedbush Securities in San Francisco.

A cautious report on technology valuations from Goldman Sachs helped ignite Friday's selling, as did a report from Bloomberg News that upcoming iPhones will use modem chips with slower download speeds than some rival smartphones.

But with the technology index up over 18 percent year to date, some investors said the selloff boiled down to straight-forward worries about valuations. They questioned whether the technology sector's rally may be coming to an end. "You have to be ready to make a sale if the momentum changes," warned Phil Blancato, head of Ladenburg Thalmann Asset Management in New York. "When it starts to erode, it could erode very quickly."

The information technology index recently traded at 18.4 times expected earnings, the highest level since the 2008 financial crisis, according to Thomson Reuters Datastream.

Software company Cloudera tumbled 15.72 percent after its earnings report, while Wall Street favorite Nvidia Corp slumped 6.46 percent to $149.60 after short seller Citron Research said the stock could trade back to $130.

The decline in Nvidia, by far the top-performing stock in the S&P 500 over the past year, contributed to a 4.23 percent drop in the Philadelphia Semiconductor Index, its worst day in nearly a month. Over the past 12 months, Nvidia has surged 216 percent.

Technology stocks are likely to remain under pressure until second-quarter earnings reports provide a new potential catalyst, predicted Wedbush trader Joel Kulina.

The sector showed signs of support late in Friday's session, with the Nasdaq reducing some of an earlier 2.9-percent loss. That reinforced some investors' expectations that the technology rally still has legs.

"It signals that there's still money on the sidelines waiting to come in and buy the dip," said Bucky Hellwig, senior vice president at BB&T Wealth Management in Birmingham, Alabama. "Money should come back into the stocks because investors are still looking for growth."