Shares of Qualcomm were up 1% at $65.25 in premarket trading, while those of Broadcom fell 0.7% to $263.

“After a comprehensive review, conducted in consultation with our financial and legal advisors, the Board has concluded that Broadcom’s proposal dramatically undervalues Qualcomm and comes with significant regulatory uncertainty,” Qualcomm’s Presiding Director Tom Horton said in a statement.

Broadcom made its unsolicited bid last week in its efforts to become the dominant supplier of chips used in the 1.5 billion or so smartphones expected to be sold around the world this year.

Reuters reported on Sunday that Qualcomm would rebuff the $70 per share offer, citing people familiar with the matter.

Broadcom could not immediately be reached for comment.

The offer also comes at a time when Qualcomm is trying to close its pending $38-billion acquisition of automotive chipmaker NXP Semiconductors NV.

Broadcom has indicated it is willing to buy Qualcomm irrespective of whether it closes the NXP deal.

A sale to Broadcom would also need a nod from the antitrust officials, who are still considering Qualcomm’s purchase of NXP.

Qualcomm, an early pioneer in mobile phone chips, supplies so-called modem chips to phone makers such as Apple, Samsung, and LG that help the phones connect to wireless data networks.

“No company is better positioned in mobile, IoT, automotive, edge computing and networking within the semiconductor industry,” Qualcomm’s Chief Executive Steve Mollenkopf said. “We are confident in our ability to create significant additional value for our stockholders.”