Broadcom's proposal last week represented a 28 percent premium over the closing price of Qualcomm shares on November 2, but analysts were expecting Qualcomm the reject the $70-per-share bid.
"It is the board's unanimous belief that Broadcom's proposal significantly undervalues Qualcomm relative to the Company's leadership position in mobile technology and our future growth prospects", executive chairman Paul Jacobs said in a release.
Presiding Director Tom Horton also cited "significant regulatory uncertainty" around the proposed deal. If shareholders want a deal, they could vote for new board members and force the company to come to the negotiating table.
ZDNet has reached out to Broadcom and will update if we hear more.
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Qualcomm recommended shareholders spurn the deal, saying it's an opportunistic move by Broadcom to buy the wireless-chip maker on the cheap.
Qualcomm provides chips to carrier networks to deliver broadband and mobile data.
NXP shares have been trading above Qualcomm's offer price, as many NXP shareholders, including hedge fund Elliott Management Corp, have been holding out for a better price.
A sale to Broadcom would also need a nod from the antitrust officials, who are still considering Qualcomm's purchase of NXP.
Qualcomm shares closed at $64.57 on Friday, while Broadcom ended at $264.96.