Allegro MicroSystems (ALGM) said Thursday it received an unsolicited acquisition offer from ON Semiconductor (ON) but determined that "the proposal was inadequate."

ON Semiconductor said late Wednesday it proposed to acquire Allegro for $35.10 per share in cash for an implied enterprise value of $6.9 billion.

ON Semiconductor said it has "made numerous attempts" over the last six months to enter acquisition talks with Allegro.

"While we would have preferred to reach an agreement with Allegro privately, the decision to make our proposal public reflects our conviction in the merits of a combined company, which we believe is in the best interests of Allegro and Onsemi shareholders," said Hassane El-Khoury, president and chief executive officer of ON Semiconductor.