When it comes to the stock market, Silicon Valley is richer than ever before. But how high is too high?
Amazon hit a fresh all-time high on Thursday — and also Wednesday,
But if earnings and revenue growth don't stay at a sustainable pace for the next five to seven years, "all bets are off," said Chad Morganlander, a portfolio manager at Washington Crossing Advisors.
Buoyed by broader market gains, the tech giants also have been boosted by better-than-expected quarterly earnings. All three beat Wall Street's estimates for adjusted earnings per share in the latest quarter.
"The reason a lot of these tech companies have moved quite to the upside is that revenue growth has been strong as well as earnings have been strong," Morganlander told CNBC's "Squawk Alley" on Friday. "Money managers are crowding into that trade to try and beat their benchmarks."
But Morganlander said that when comparing some tech stock prices to their earnings and sales, the valuations are starting to look lofty.
"Apple, I wouldn't say is super-rich," he said. "But when you start looking at a Netflix, an Amazon, or a Facebook ... then you're starting to get into nosebleed territory. So buyer beware here."
While technology companies have grown somewhat unfathomably large — picture Apple's $256.8 billion cash hoard — they have done so on the secular trend of digitization, said Kate Mitchell,
"It's always a risk — these are getting pricey," Mitchell told "Squawk Alley" on Friday. "It's interesting watching these companies. They're starting to establish, on a relative basis, incredible dominance not only from a pricing standpoint ... but within their markets. Look at what's happening to retail. Look at what's happening to the auto companies, as a contrast. They are moving farther ahead of the companies they're competing against, and they're using tech to do that."
While Amazon opened a swanky New York City bookstore this week, many retailers are shuttering their brick-and-mortar locations. Technology has played a role: Latest research from Goldman Sachs shows that cashier is one of the professions at the highest risk to have jobs lost to automation.
Morgan Stanley this week released a report on another longer-term trend, self-driving vehicles. But of the 30 U.S. stocks set to benefit, many were not traditional automakers.
As technology companies have continued to disrupt businesses outside the technology sector, the rest of the S&P 500 has been "shaking in their boots," Mitchell said.
"Yes, I think it would be painful if it reversed," Mitchell said. "But I think obviously what people are buying is growth ... I think the question you have to ask is, 'Is it overbought?'"
Nobel Prize winner Robert Shiller doesn't seem to think so. Shiller, credited with foreseeing the dot-com bubble of the late 1990s, told Fortune on Friday that the tech sector is relatively undervalued.
"We make an adjustment for the fact that technology stocks have always been highly priced, so recently they've been less highly priced overall than on average," Shiller said.
Tech may be benefiting now. But Morganlander said that large-scale changes — such as interest rate adjustments and shifts in international economic growth — could hit the market over next 18 months, he said. "Old world tech" companies like Oracle and Microsoft could provide more predictable investments, he said.
"You saw that, back in the late '90's into the early 2000s," Morganlander said. "Not that we're in a bubble yet, but we have to, of course, be much more circumspect and cautious."
Disclosure: Washington Crossing Advisors is a subsidiary of Stifel Financial. Stifel or an affiliate makes a market in shares of Apple, Microsoft, Oracle, Amazon, Facebook,