Lei Xu and Justin Song once worked at electric carmaker Tesla Inc, one of the hottest companies in Silicon Valley. But with interest and investments in autonomous vehicles mounting, they left to pursue what they see as the next big thing.

Their company, Nullmax, is one of more than 240 start-ups worldwide, including 75 in Silicon Valley, attempting to design software, hardware components and systems for future self-driving cars, according to a Reuters analysis.

Xu and Song are bankrolled by corporate money, but unlike many of their fellow entrepreneurs, they skipped funding from Silicon Valley venture capitalists. Founded in August 2016, Nullmax got $10 million from a Chinese firm, Xinmao Science and Technology.

By seeking corporate backing in China, the Nullmax founders managed to sidestep an issue facing other startups in the sector. While big automotive and technology companies are pouring billions into the autonomous vehicle space, Silicon Valley investors so far have been fairly restrained in increasing their bets.

Headlines have been dominated by old-line players such as General Motors, which jolted the industry last year when it bought a tiny San Francisco software company called Cruise Automation for a reported $1 billion. Just last week, top-tier supplier Delphi Automotive acquired Boston-based software start-up nuTonomy for $450 million.

Now, “every start-up thinks they will get a billion dollars” in valuation, said Evangelos Simoudis, a Silicon Valley venture investor and an adviser on corporate innovation.

Investment in untested start-up companies remains relatively modest despite all the buzz and lofty expectations

However, investment in untested start-up companies remains relatively modest despite all the buzz and lofty expectations. Total funding of self-driving start-ups from both corporate and private investors has barely topped $5 billion, the Reuters analysis of publicly available data shows.

With the notable exceptions of Andreessen Horowitz and New Enterprise Associates, few of the big Valley venture capital firms are heavily invested in the sector.

Overall, only seven of the top 30 self-driving start-ups have received later-stage funding, the Reuters analysis shows, an indication that some venture capitalists are ambivalent about the industry’s potential.

Sceptics note that few of the startups are making money. And  established auto and parts companies have not demonstrated a clear path to revenue and profitability in autonomous vehicles despite their big bets in the space.

Another sticking point: while the initial wave of self-driving vehicles is expected to begin commercial service in 2019-2020, experts expect the transition from human-driven to automated cars could take a decade or more to roll out.

Sergio Marchionne, chief executive officer of Fiat Chrysler Automobiles cautioned: “You can destroy a lot of value by chasing your tail in autonomous driving.”

All told, US automotive and technology firms likely have invested some $40 billion to $50 billion in self-driving technology in recent years, mainly through acquisitions and partnerships.

The full extent is hard to know because big players such as Alphabet Inc, whose Waymo subsidiary is considered among the front-runners in the arena, have not revealed the full scope of their investments, although it is believed to be in the billions.