FRANKFURT (Reuters) - Private equity groups Bain and Advent are doing thorough due diligence on Osram <OSRn.DE> in preparation for a potential takeover offer, Olaf Berlien, the Chief Executive of the German lighting maker said on Thursday.
Bain and Advent said in a letter on last month they were prepared to make an offer for Osram at a price "meaningfully" above that of rival bidder Austrian sensor specialist AMS <AMS.VI>.
"I hope it was not a joke", he said referring to the letter which effectively derailed AMS's offer.
"To make it clear, I think there are huge teams in the data rooms. I'm quite sure (of Bain and Advent being serious about this) if they spend the money," he said on a call with analysts.
AMS's 4.5 billion euro ($5 billion) takeover offer for Osram fell through last week, but AMS said it would still explore strategic options to pursue an acquisition of the German lighting group after securing a 20% stake.
AMS had sweetened its bid to 41 euros a share after Bain and Advent said that they were prepared to trump the Austrian group's original offer of 38.50 euros.
Berlien said he was open to a potential new offer from AMS, adding that the terms needed to be right.
He also said he did not tender his shares in AMS' tender offer as some of Osram's concerns had not been addressed while the offer price was not the issue.
(Reporting by Arno Schuetze. Editing by Jane Merriman)