Shares of the Seoul company at last check were 12% higher at $25.70. In 2021 through the close of Thursday trading, the stock had been up 70%.
Magnachip said the offer came from Cornucopia, the London investment firm, on behalf of itself and an investor group. The bid values the company at $1.66 billion.
The investors include financial sponsors led by Tim Crown, chairman and former chief executive of Insight Enterprises (NSIT) - Get Report, Yango financial holdings, Sino-Rock Investment Management Co. and Lombarda China Fund.
In March, Magnachip agreed to be acquired by the Beijing investment firm Wise Road Capital in a transaction valued at $1.4 billion.
Under that agreement, Magnachip holders would receive $29 cash for each of their shares.
Magnachip said the board would review and consider Cornucopia's proposal.
The company said that it had the right to participate in discussions with Cornucopia through June 16 for the sole purpose of determining "whether the proposal constitutes or could reasonably be expected to lead to a superior proposal."
Magnachip's board "has not yet made such a determination," the company said.
In light of the proposal, Magnachip said it expects to adjourn a special meeting of stockholders that had been set for June 15 through 17.
The company said that it remained subject to the merger agreement and that its board has not changed its recommendation that Magnachip stockholders vote for the proposal to adopt the agreement and approve the merger.