Siemens AG has hired UBS to help sell its hearing-aid unit, with initial teaser documents on the business likely to reach bidders before Christmas, sources familiar with the matter said.

Siemens hopes the unit, which competes with Switzerland's Sonova Holding AG and Denmark's William Demant Holding A/S, could fetch about 2.5 billion euros ($3.77 billion), one of the sources said.

Bidders may include major private equity firms such as BC Partners, KKR, Carlyle, Cinven and CVC, some of the sources said.

Last week two sources close to the matter said several financial investors, including KKR and BC, were interested in the unit.

Siemens declined to comment.

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(Reporting by Quentin Webb and Zaida Espana in London, Philipp Halstrick in Frankfurt and Jens Hack in Munich; Editing by Joel Dimmock)

($1=.6635 Euro)