Veeco Instruments Inc.’s agreement to acquire California-based Ultratech Inc. includes a $26.5 million termination fee, according to a government filing released Friday.

The acquisition agreement also would allow Ultratech to accept “an unsolicited superior proposal” under certain circumstances, and either party could terminate the merger agreement if the deal is not closed by Oct. 17, the Securities and Exchange Commission filing said.

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Ultratech would be required to pay the termination fee to Veeco if it accepts a better offer or if the deal is canceled under certain other conditions.

On Thursday, Plainview-based Veeco announced it had agreed to acquire Ultratech for $815 million in cash and stock. Veeco said the deal’s value is about $550 million, net of Ultratech’s net cash balance as of Dec. 31.

Ultratech, based in San Jose, makes lithography, laser-processing and inspection systems used to manufacture semiconductor devices and light-emitting diodes. Veeco produces tools to make LEDs, hard drives and chips for wireless devices.

The merger must be approved by regulatory authorities and holders of a majority of Ultratech’s outstanding stock.

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Shares of Veeco climbed 3.7 percent to $25.78 at midday Friday, while shares of Ultratech rose 0.7 percent to $28.40.