Apple Inc. is playing the role of kingmaker in the contentious battle for Toshiba Corp.'s memory chip business.

The iPhone maker is in talks to provide about $3 billion in capital for Bain Capital's bid for the unit, adding to financial support from Dell Inc., Seagate Technology PLC and SK Hynix Inc., according to people familiar with the matter. That support convinced Toshiba to sign a memorandum of understanding with Bain and work toward a final agreement this month, said the people, asking not to be identified because the matter isn't public.

Apple plans to take an equity stake alongside Bain, they said. If the agreement is completed, it may exceed Apple's largest deal ever, the $3 billion acquisition of Beats Electronics LLC.