Recent sharp increases in the valuation of young technology companies have some experts arguing that a repeat of the late 1990s tech bubble is upon us.

Social media giant Twitter, for example, has seen its stock price soar 165 percent since its Nov. 6 initial public offering without any apparent change in company fundamentals.

But Marc Andreessen, co-founder of venture capital titan Andreessen Horowitz, doesn't see excessive froth among software companies.

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"There's no bubble, per se," he tells The Wall Street Journal.

"Bubbles are a very specific phenomenon where you've got mass psychology and you've got every mom-and-pop investor and every cabdriver and every shoe-shine boy buying stock in whatever it is — going all the way back to the South Sea Bubble all the way through to the dot-com bubble."

That's not what's happening now, he says. "We're talking about a fairly small number of companies. And then, we're talking almost entirely on the private side. It hasn't really affected the public market that much."

So what's different now from the dot-com bubble period?

"The costs of building an Internet company today are far lower than they were in the late '90s," Andreessen explains.

Still, many see a shakeout coming.

"What's likely to happen is that there will be a huge winner-takes-all outcome, where one or two companies and investors will be successful," David Santschi, chief executive at TrimTabs Investment Research, tells The New York Times.

"But as a result, there will be a lot of companies that are just going to go poof."

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