Natel Engineering Co. announced on Monday it would merge with OnCore Manufacturing LLC to create one of the largest microelectronic assembly firms in the United States.

The combined operations of Natel, in Chatsworth, and OnCore, in Fremont, will have more than 3,700 employees in 13 locations and revenue topping $700 million. The deal is expected to close next month.

“This is a compelling strategic combination that creates a market-focused leader in the high-reliability mid-tier space,” said Natel Chief Executive Sudesh Arora in a prepared statement.

The merger was financed by Goldman Sachs Bank USA and GE Capital Corp. B. Riley & Co. LLC, in Los Angeles, was the company’s financial advisor

Founded nearly 40 years ago in Van Nuys as a defense contractor, Natel has built up its microelectronic assembly capabilities through acquisitions, the most recent in 2013. Microassembly involves the manipulation of microscopically small parts.

The company supplies customers in the medical, aerospace and defense, and industrial markets with electronic subassembly components. It has facilities in Carlsbad and four other states, as well as Mexico.

OnCore was founded in 2007 through the consolidation of four separate manufacturing companies. It serves aerospace, defense, industrial and medical companies from facilities in California, Colorado, Illinois, Massachusetts, Mexico and China.

“We are highly complementary organizations and our combined value proposition will deliver competitive advantages for our customers,” said OnCore Chief Executive Sajjad Malik in a prepared statement.