DoorDash, the on-demand delivery service valued at $4 billion, has leased more office space in San Francisco as it continues to compete with hometown rivals Postmates and Uber.

The 193,000-square-foot deal at 303 Second St., one of the city’s largest this year, shows an unabating boom in tech jobs that has made San Francisco one of the country’s most expensive places for real estate.

Building owner Kilroy Realty Corp. said in a news release on Wednesday that it had signed a long-term deal with a tech tenant in the South of Market neighborhood, but didn’t provide details. Two sources with direct knowledge of the deal who weren’t authorized to speak publicly confirmed the transaction was with DoorDash. Kilroy and Doordash didn’t respond to requests for comment.

“This lease underscores the intense demand that exists for high quality, well-located, large blocks of space among San Francisco’s creative companies whose expectations have risen dramatically as they face increasing competition for top talent,” Kilroy said in the release.

The new tenant will move into 303 Second St. as existing tenants move out between 2019 and 2021, John Kilroy, CEO of Kilroy, said in an earnings call Thursday. The new lease has rents that are 56 percent higher than existing deals, he said.

Kilroy, one of the largest owners of office space in San Francisco and the West Coast, reported a total of 2.6 million square feet in its portfolio from July to September. In the past year, it has signed deals with San Francisco tech firms like Adobe, Cruise and Dropbox.

West Coast office market fundamentals are “the strongest we’ve ever seen driving robust demand for real estate from both tenants as well as buyers,” John Kilroy said on the call.

DoorDash was founded in 2012 by UC Berkeley and Stanford students. The company raised $535 million in March and another $250 million in August, valuing the privately held company at $4 billion.

As of March, DoorDash had 550 employees and was aiming to grow to 800 employees. The space at 303 Second St. has room for over 1,000 employees. The company’s drivers who deliver food and other products to customers are independent contractors.

There are now around 150 job listings, mostly in San Francisco, on the company’s website.

DoorDash currently has space at 901 Market St., 116 New Montgomery St. and 233 Eddy St. It isn’t clear if it will vacate those buildings.

“To lock in space that is desirable to today’s millennial workforce, companies are having to be flexible in how they acquire space, often times, committing to leases a few years out,” Kilroy said in the release.

Roland Li is a Chronicle staff writer. Email: roland.li@sfchronicle.com Twitter: @rolandlisf