Siltronic last month announced it was in advanced talks to be bought by GlobalWafers in a 3.75 billion euro ($4.55 billion) deal it described as "appropriate and attractive".

While the offer price represented a 48% premium to the undisturbed average 90-day average share price, the gap narrowed in the days before the news broke, with Argonaut complaining of being short-changed.

"Siltronic minority shareholders are being corralled into selling out at a cyclical bottom in the semiconductor wafer industry," Barry Norris, CEO and fund manager at Argonaut, wrote in an open letter to Siltronic Chairman Tobias Ohler.

Siltronic is the largest position in Argonaut's Absolute Return Fund.

"The premium offered is a very modest 11%. We therefore believe that this claim is misleading to Siltronic shareholders as to the generosity of the control premium on offer and should be withdrawn," Norris said in the letter.

Siltronic described the allegations as baseless, saying it was being fully transparent on the discussions with GlobalWafers and that it still considered the proposed offer price of 125 euros per share to be attractive.

Argonaut noted that the parent company of GlobalWafers is Sino-American Silicon Products, a major customer of Germany's Wacker Chemie, which itself is expected to tender its 30.8% stake in Siltronic under the proposed scheme.

"There is potential for a perceived conflict of interest," Norris wrote in the letter to Ohler, who is also chief financial officer at Wacker.

Wacker declined to comment.

($1 = 0.8247 euros)

(Reporting by Douglas Busvine and Alexander Huebner; Editing by Emma Thomasson, Alexander Smith and David Goodman)