Did someone mention market froth? The number of stocks soaring 100 percent or more on their first day of trading is at their highest level since the IPO craze of the dot-com boom – which of course ended badly.

Nine IPOs have doubled in price on their first trading day in the past nine months, USA Today reported. Prior to that, only five IPOs had done so in the past 12 years.

Healthcare companies, including biotechs, have been at the forefront of IPOs in 2014, with 25 of the total 45 U.S. offerings so far this year coming from that industry.

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Renaissance Capital reported nine IPOs are expected to price this week, including companies in software, online banking and networking.

USA Today said one unanswered question is whether tech entrepreneurs will continue to be lured by the receptive IPO market, like they were during the dot-com craze, or choose the safer route of selling out to a large company, like WhatsApp did with Facebook recently.

Jay Ritter, professor of finance at the University of Florida, said, "Tech is even riskier today with the half-life of products getting shorter. Remaining an independent company has a lot of risks."

Some new companies in 2014 are raising their initial per-share pricing before launching – a sign of strong demand. Another sign of IPO popularity is the fact the new offerings are up an average of 17 percent in their first day of trading so far this year.

However, while the hotter IPO market may make it appear the dot-com boom is back, USA Today said that's not really the case. During its heyday in 1999, 177 IPOs doubled on their first day, and 77 did so in 2000.

That's a far cry from this year's nine, although 2014 is not over yet.

Renaissance Capital said the number of IPOs filed — many of which have not yet priced — is already at 81 for the United States, up 237.5 percent from 2013.

So far, all of the IPOs that have successfully launched in 2014 have returned an average of 37.7 percent, a strong result.

The hot IPO market this year is actually a global phenomenon, according to Renaissance Capital. It estimated there have been 59 IPOs priced worldwide — roughly double the number at the same time last year — and total proceeds have been $28.3 billion, up 96.3 percent from 2013.

The IPO market in Europe, especially among biotech companies, is also heating up Reuters reported.

"There is growing noise suggesting the IPO market is opening up in Europe and, in fact, it would be surprising if it didn't. There is normally a lag of about a year from the U.S. taking off and Europe following," said Francesco De Rubertis, a biotech investor at Index Ventures in London.

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