Uber CFO steps down after huge year of financing

Uber's chief financial officer is stepping down after nearly two years of leading financing rounds that have seen the ride-hailing service become one of the most valuable venture-backed startups.

The departure of Brent Callinicos was revealed Monday in an email sent to investors by Uber CEO Travis Kalanick. Callinicos will remain on temporarily as an advisor, according to Kalanick's email, confirming a report published by The Wall Street Journal. The departure comes as the startup is widely thought to be preparing for an initial public offering.

"Almost two years ago, I brought on one of the great financial operators in Silicon Valley as our CFO," Kalanick said in his email. "Though two years sounds short, Uber was a much smaller startup then -- about one-tenth the size we are today. Brent has provided critical leadership to take Uber to the next level as we matured as a company."

Noting that working at a startup like Uber requires significant endurance and sacrifice, Kalanick's email indicated that Callinicos' decision was based on a desire to spend more time with his family.

"Brent has done a wonderful job here at Uber but has decided that it is time for his next journey, one where his wife and daughter take the front seat," Kalanick wrote.

Under Callinicos, the San Francisco-based startup has closed several hefty rounds of financing. The service, which lets drivers connect with passengers via a smartphone app, is now the second-highest valued venture-backed company in the world with a valuation of $41.2 billion.

Over the course of the past year, the company raised more than $2.4 billion, including the most recent round of $1.2 billion in December. In January, Uber also received a round of $1.6 billion in convertible debt financing from wealth management clients at Goldman Sachs. The only company with a higher valuation than Uber is Chinese smartphone-maker Xiaomi, which has a valuation of $46 billion.

Callinicos managed that hefty fundraising despite waves of bad publicity over the past few months. Critics have said Uber unfairly competes with its rival Lyft. The company, which is currently in more than 260 cities in 54 countries, has also battled regulators in the US, Asia and several countries in Europe. Additionally, some of its drivers have allegedly attacked passengers, raising concerns about whether driver background checks are strict enough.

Callinicos joined Uber in September 2013 after six years at Google, where he served as treasurer and chief accountant. Before joining Google in 2007, Callinicos spent 14 years at Microsoft. Gautam Gupta, whom Kalanick described as Callinicos' "right hand" in strategic finance, will fill in as the head of finance, although no permanent replacement was named.

CNET's Dara Kerr contributed to this report.