[Your letterhead, if desired; if not, your return address]

[Date of letter-month, day, and year]

[Recipient's first and last names]
[Company name]
[Street or P.O. box address]
[City, State ZIP code]

Dear [recipient's name]:

This summer's internship with your company has been a truly incredible experience, and I thank you for this excellent opportunity. The internship has allowed me to learn, expand my skills, and revise my future career goals. I know the experience that you have provided will affect me for years to come.

Thank you again for this invaluable opportunity. I look forward to staying in touch with you and your staff members.

Best regards,

[Signature]

[Sender's first and last names]