The former eBay chief executive had spent nearly $100 million on her primary and general election contests through the end of June, making it the most expensive campaign in California history.
Her Democratic rival, state Attorney General Jerry Brown, has spent just $774,000, including donated services, although union-backed groups have spent nearly $6 million on ads supporting him. The latest is scheduled to begin airing Monday.
Public opinion polls show the two are locked in a dead heat, with nearly a quarter of voters still undecided.
Word of Whitman's most recent contribution came in a filing late Friday with the secretary of state's office.