The market caps of all the public ad tech companies combined isn't even half the size of Criteo's

If you asked anyone in ad tech to name the star-performer of the sector, most people would point to Criteo.

Criteo is the France-based ad tech company that specializes in "performance" advertising.

It works with ecommerce companies to target ads at people who are likely to be in the market for buying their products - mostly through a method called retargeting, which serves ads to people who have already viewed that particular brand's product, website, or a competitor product or website.

Last year, Criteo's CEO Eric Eichmann explained why it's not like other ad tech companies (and why it's outperforming many of them): It focuses on one thing and does it well, it works directly with clients rather than agencies, and it has the scale to drive competitors in the space out of the market.

It's clearly working. On Wednesday, Criteo reported a 36% increase in revenue to $407 million and an adjusted EBITDA rose 66% to $39 million.

Here's one way of looking at how Criteo is outperforming the ad tech market: If you add together the market caps of all the public ad tech companies, that number doesn't even come to half of Criteo's market cap:

Here are the numbers (correct as of 12 p.m. GMT August 5):

• Criteo: $2.59 billion
• TubeMogul: $410.33 million
• Rubicon Project: $316.05 million
• YuMe: $120.75 million
• Rocket Fuel: $105.86 million
• Marin Software: $104.34 million
• Tremor Video: $100.15 million
• Maxpoint Interactive: $71.47
• The combined total of all public ad tech companies minus Criteo: $1.22 billion

An added bonus: Here's how the ad tech stocks performed in the second quarter of this year. You'll notice Maxpoint Interactive had a strong performance, but that followed a reverse stock split.

Retargeting may be sniffed at by some in the advertising community as the "pair of shoes you already bought that keep following you around the internet," but it's clearly working for Criteo.