Facing a takeover proposal from a secretive fund, Tsinghua Unigroup Co.’s chairman has vowed to "fight to the end” — amplifying an unusually public dispute over the troubled chipmaker’s $9 billion rescue plan.

Zhao Weiguo, whose company controls 49% of the debt-ridden semiconductor giant, is doubling down on a rare outburst this month against a takeover bid led by JAC Capital.

Jiankun, Zhao’s holding firm, is now intent on unearthing the backers behind JAC, a fund headed by reclusive financier Li Bin that had kept a low profile until its consortium emerged as Unigroup’s winning bidders, the executive said in an interview Tuesday.