The banner year of initial public offerings in 2014 came with a disappointing twist: The class of newly public tech companies has, on the whole, paltry revenue and little sign of making a profit.

Thirty-four Bay Area tech companies had an IPO last year, the most the region has seen since the dot-com boom. And yet just five of these companies were making enough money to join the SV150, this newspaper’s annual ranking of the largest companies in Silicon Valley, measured by sales. While valuations are soaring and investors are writing checks faster than startups can cash them, it’s not all sunshine and fairy tales in the tech market: Some tech companies are going public prematurely, analysts say, while others are simply riding the recent biotech craze and may be risky bets.

“Why did some companies go public? Because they could,” said Sam Hamadeh, founder and CEO of PrivCo, a financial data provider on private companies. “The market was frothy enough that they wanted to get it while it was hot. It was purely opportunistic. For a lot of these companies, it didn’t matter that they weren’t ready.”

In theory, it should have been fairly easy for more of the 34 Bay Area firms to make the SV150, which comprises tech companies with annual revenue of at least $150 million. Some analysts say a general rule of thumb for companies going public is they ought to have $250 million in annual revenue, or in healthy markets such as this one, that benchmark slides to roughly $100 million. If for no other reason, companies need the revenue because the cost of going public is steep.

But nearly two-thirds of the Bay Area tech companies that had IPOs in 2014 didn’t even meet that $100 million revenue threshold. And just 15 percent of them were added to the SV150, the lowest percentage in at least 13 years, according to historic SV150 data. Generally, it’s closer to 36 percent.

The Bay Area companies that held an IPO in 2014 and joined the SV150 are GoPro, the action-sports camera maker from San Mateo; Arista Networks of Santa Clara, a cloud-computing company that serves high-speed data centers; San Francisco-based Lending Club, the first IPO from an online lending startup; Mountain View-based digital coupon company Coupons.com; and application networking company A10 Networks of San Jose. GoPro led with $1.4 billion in sales last year, securing the 51st spot on the list, ahead of more senior SV150 members such as Dolby and Zynga.

Not one of the Bay Area biotech firms made the list, although they accounted for nearly half the IPOs last year. Many have low revenue and several have never made a sale, often because the drug they make hasn’t been approved. For instance, Dermira, a Menlo Park firm developing dermatology treatments, raised $125 million in its October IPO, and last year posted $32 million in losses.

“The revenue averages were dragged down on what was a banner year for IPOs,” Hamadeh said.

Indeed, the median revenue of all Bay Area IPOs last year was $51 million. In 2013, the median revenue was $131 million, and in 2012 it was $144 million, according to an analysis of data from FactSet and Ipreo, a market intelligence firm.

Biotech companies rushed to Wall Street simply because, for the first time in years, they could, say experts. Public companies such as Gilead Sciences and Pharmacyclics got federal approval for breakthrough drugs that began selling at steep prices, and investors began furiously buying stocks. The public market, having recovered from the beating in 2008, is now more receptive to risky companies — such as biotech firms that haven’t yet made a sale.

“More than any other industry, biotech was completely out of favor, then all of a sudden the gate is open, the door is open and the windows are open,” said Paul Boyd, managing director of ClearPath Capital Partners, a wealth management firm in San Francisco.

Biotech isn’t all to blame for the lower revenues among IPOs. More tech companies overall are going public with losses than anytime in 14 years. Last year, nearly 65 percent of the tech companies that had an IPO of more than $100 million did not have any profits, the most since 2000, when close to 75 percent of IPOs were unprofitable companies, according to data from ClearPath Capital. Three of the five companies that joined the SV150 — Lending Club, Coupons.com and A10 Networks — didn’t have a profit last year.

Some experts say the JOBS Act has encouraged more young and challenged companies to go public before they are ready. The law, signed in 2012 to encourage funding of small businesses, opened the door for companies to file for an IPO confidentially, allowing them to keep their financial details private for a period of time and providing of an incentive to make a public offering.

But companies such as Lending Club and Arista Networks say an IPO was exactly the right decision. Arista Networks, founded in 2004, is entirely self-funded and has been profitable since 2010.

“We didn’t have VCs to satisfy and we didn’t have any outside pressure to do any unnatural acts,” said Mark Foss, Arista’s vice president of global operations. “We had all of the correct profits. (The IPO) just gets us exposure at the global level.”

Lending Club didn’t need the cash from an IPO, said chief executive Renaud Laplanche, but it did need to build the public’s trust in the emerging online lending business. As a public company, Lending Club can prove to consumers — and to the banks it competes with — that it wasn’t going anywhere.

“When you deal with financial services and people’s money, there is a really big trust factor,” Laplanche said. “Many people heard of Lending Club for the first time when we went public. We are signaling to the customers and the world that we are here to stay.”

Contact Heather Somerville at 510-208-6413. Follow her at Twitter.com/heathersomervil