Broadcom raised its bid for Qualcomm to $121 billion, sweetening an offer that already stands as the largest tech transaction in history. Broadcom called its offer its “best and final.”

Importantly, as CNBC reported, Broadcom offered to pay up to $10 billion to Qualcomm if regulators kill the deal—that amount represents a larger-than-normal breakup fee and likely is geared toward getting Qualcomm’s management to accept Broadcom’s unsolicited offer.

“Broadcom believes this offer is vastly superior to Qualcomm's standalone prospects, with or without the closing of the NXP transaction, and remains hopeful the Qualcomm board of directors will act responsibly on behalf of Qualcomm stockholders and engage with Broadcom on this offer without further delay,” Broadcom wrote in a release this morning.

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Qualcomm said it will “review the revised proposal to determine the course of action it believes is in the best interests of the Company and its stockholders. Qualcomm will have no further comment on the proposal until its Board of Directors has completed its review,” in a statement today.

As Reuters noted, Broadcom kept the cash part of its initial offer at $60 per share but raised the stock portion from $10 to $22 per share.

“Qualcomm and its board now have a tough decision as this is a compelling offer in our opinion,” Daniel Ives of GBH Insights told Reuters.

Qualcomm in November rejected Broadcom’s initial $103 billion offer for the company, arguing it undervalued Qualcomm. And last month Qualcomm argued it can generate long-term annual revenue growth of 6%-8%, and that the company’s serviceable addressable market (SAM) will grow by a factor of 6x from 2015 to 2020, to a total of $150 billion.

In any event, a transaction between Broadcom and Qualcomm would likely face significant regulatory concerns as would it combine two of the world’s largest providers of silicon. Indeed, as Reuters noted, the FTC last month made a second request for information on Broadcom’s bid.

To be clear, Broadcom isn't the only source of concern for Qualcomm's management. Apple -- which is embroiled in a patent-licensing battle with Qualcomm -- is reportedly considering dropping Qualcomm entirely as a supplier for the iPhone in favor of Qualcomm rival Intel.

Qualcomm is a leading provider of wireless technologies as well as the world's largest vendor for smartphone chips.