For the past few years, Silicon Valley seems to have done nothing but mint tech icons with eye-popping valuations.

And 2015 was no exception, as the year achieved a kind of milestone with 142 unicorns, startups so-named because their valuations have soared to the $1 billion mark and beyond. Nearly half--67 to be exact--joined the list this year, according to venture capital research company CB Insights.

In fact, there are more unicorns now than at any other time in the past four years, thanks in part to free-flowing venture capital, and investors seeking big payoffs for companies they hope will be the next Facebook or Google.

Still, if you're looking to join this mythical club, recent events suggest you better work fast. More realistic valuations seem to be chasing down this herd. One example is messaging app Snapchat, the darling of the tech world that slapped away a $3 billion offer from Facebook in 2013, only to see its valuation climb to $16 billion. Mutual fund company Fidelity in September reportedly knocked 25 percent from the value of its investment in the messaging app company. And it's likely that Fidelity, and other institutional investors, will continue to mark down investments in such companies in the coming months. 

A Wider Problem

Meanwhile, Snapchat's loss is a trend that's been repeated for the past few months with other tech companies, including cloud storage company Dropbox and soon-to-go-public Square, whose private valuations are also under downward pressure.

"All of the private market valuations are going to more closely match what the public markets actually will pay, and the two will come closer together," says Ross Fubini, venture partner at Canaan Partners, in Menlo Park, California.

Unlike their more seasoned peers, whose valuations have soared into the tens of billions of dollars, this year's flock of unicorns have somewhat smaller price tags. The list tops out at $4.5 billion, a slot awarded to human resources software maker Zenefits. Even Uber competitor Lyft, No. 2 in the ride-sharing world, comes in at $2.5 billion, a fraction of Uber's $50 billion valuation.

And here's something else to consider: In 2015, 40 percent of the new unicorns hailed from countries besides the U.S. Indeed, half of the non-U.S. companies were Chinese. So, while the unicorn phenomenon has been unique to the U.S., it may ultimately migrate overseas.

Certainly lots of investor cash has helped lever valuations ever skyward. As of the third quarter of 2015, about $47 billion in venture capital flowed into 3,329 deals, according to the National Venture Capital Association. That compares with $51 billion in 4,000 deals for the full-year 2014. Total dollars invested for both years is about 70 percent higher than total amounts invested in both 2012 and 2013.

What's in Common

And for those looking for through lines they can duplicate in hopes of becoming a unicorn themselves: One of the biggest attributes of the group has always been creating a "disruptive" technology that lets consumers or businesses do something they've done forever, but with greater ease and more cheaply. (Think Airbnb and Uber, which have re-envisioned the hotel and taxi industries, respectively.) Many also put a key component of their offering in the cloud, which dramatically reduces costs and expands reach and scale.

Two examples from this year's list are e-commerce companies Warby Parker and Blue Apron, which are currently valued at $1.2 billion and $2 billion, respectively. Blue Apron, for example, gives consumers subscription access to home delivery of farm-fresh and organic goods with instructions on how to cook meals. Warby Parker uses a slick website and a generous, free-return shipping policy to make glasses shopping pain free--and even glamorous.

Yet others occupy a place between consumers and the red-hot biotech and health care sectors. 23andMe, founded by Anne Wojcicki, ex-wife of Google co-founder Sergey Brin, is but one example. The company's home DNA kits test for inherited genetic illnesses and build a large database of genetic attributes that could be useful in combating a wide range of diseases.

Online alternative lending companies are also well-represented this year, from personal loans for people with less than perfect credit, as served by Avant, to small business loans from Kabbage and Prosper. So are media upstarts, represented by Buzzfeed and Vice Media, with values of $1.5 billion and $2.5 billion, respectively. Both have created novel approaches to media, combining news, entertainment, and social networking.

Going forward, Fubini says, new unicorns will have to make sure they're not only disrupting old ways of doing things, but that their technology is unique to them, and that they have airtight business models that can make them money.

Here are a few other newly minted unicorns from 2015 that are worth watching in 2016.

1. GitHub

The San Francisco company is a web-based repository and hosting service for public software code. It became a unicorn in July, following a reported $250 million Series B round from Sequoia Capital, which gave it a $2 billion valuation. 

2. Oscar Health

The New York City company provides health insurance plans through state health care exchanges, as well as medical consultations by phone. It joined the list in April and has a $1.75 billion valuation, following more than $300 million in investments.

3. Thumbtack

The online marketplace connects consumers with skilled professionals such as music teachers and plumbers. Based in San Francisco, it has a $1.3 billion valuation as of September, following a Series E round worth $125 million.

4. Twilio

This San Francisco cloud communication company lets users build VoIP and SMS applications. It has had six rounds of financing reportedly worth $234 million, and it's valuation jumped to $1.1 billion in May. Twilio is an Inc. 5000 company.

5. Vox Media

The Washington, D.C., digital media company brings consumers commentary on topics ranging from food to politics and technology through online brands such as, The Verge, and Re/code. It's raked in $300 million in venture capital over the past few years, but joined the unicorn list in August, at a $1 billion valuation, following a $200 million Series F from NBCUniversal's venture arm.

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