The plant will be located in the Quang Chau Industrial Park in the northern province of Bac Giang and will annually produce eight million units, the government said in a statement on its website.
The Taiwanese electronics contract manufacturer has so far invested $1.5 billion in Vietnam and created jobs for more than 35,000 workers and the company, formally known as the Hon Hai Precision Industry Co., plans to raise its investment by $700 million and recruit 10,000 more local workers this year, the government said.
Last week Foxconn was also looking into investing $1.3 billion in Thanh Hoa Province, 160 km south of Hanoi.
Last year, the company produced the first batch of display screens at its $26-million factory in the northern Quang Ninh Province.
Foxconn, a major assembler of Apple products, including the iPhone, and the world's largest contract manufacturer, came to Vietnam in 2007, and has been operating mainly in the northern provinces of Bac Ninh, Bac Giang and Vinh Phuc, making computers and other electronic products and car parts.
It has said that Vietnam is its largest manufacturing hub in Southeast Asia.