Your is a sample template you can use to write a thank you letter for your sponsor.
To,
[Name]
Dear, [Name]
We would like to express our immense gratitude towards your contribution to this venture. Your sponsorship has been extremely helpful for [Company name].
We would like to attribute a part of our success to your contribution as it helped us move a step forward.
Thanking you again.
Sincerely,
[Company name]