The number is expected to increase after the registration process is opened to those not affiliated to the 500 community organisations which have joined hands for the reception.
Given that the capacity of SAP Centre in San Jose - an indoor arena in the heart of Silicon Valley - is just 18,000, the Indo-American Community of West Coast, created recently to organise the reception, would have to resort to lottery to determine who all would get free tickets to attend the event.
Khande Rao Kand, convener of the Indo-American Community of West Coast, today tweeted: "25K already registered for Silicon Valley event." "Individual registrations to open next week," Rao tweeted.
In September last year, Modi addressed about 20,000 Indian-Americans at the Madison Square Garden in New York, which was also attended by about 40 top American Congressmen and Senators.
California has the second-largest population of Indian- Americans after the Tristate area of New York, New Jersey and Connecticut.
Modi is scheduled to travel to San Francisco after addressing a high-level summit on sustainable development hosted by the UN on September 25, becoming the fourth Indian Premier to visit US' West Coast.
Modi's visit to San Francisco would also revive - after a gap of four decades with the exception of the former prime minister PV Narasimha Rao in 1994 - the post-independence tradition of Indian prime ministers visiting the US cities other than New York or Washington DC.
The Indo-American Community of West Coast today also announced a Selfie Video contest.
"Record a selfie video of less than 1 minute on your idea of India - on what India means to you. The best video could win a USD 100 gift card and two guaranteed passes to the event. Selected videos will be featured on this page regularly," the organisation said on its Facebook page.