Internships are valuable opportunities to gain professional knowledge in a field that interests you, and it's very likely that you may have to provide multiple references throughout the application process. It's very important to thank the people who provide you with references, not only to show your appreciation but to maintain a quality working relationship.
Here's a sample reference thank you letter letting the reference writer know you appreciate their assistance with providing a reference for an internship for you.
If you send an email thank you letter, simply put "Thank You" and your name in the Subject line:
Subject: Thank You - Your Name
Internship Reference Thank You Letter Example
Dear Dr. Bloke,
Thank you for the reference for the Research Assistant internship in the Biology Department at City University. I appreciate your confidence in me, and your willingness to contact your colleague in my behalf. I look forward to broadening my experience through this internship, and I am deeply grateful for your effort.
I look forward to working with you on my senior thesis, and I believe that the experience at City U would give me an interesting perspective with which to approach my own research.
Again, thank you very much. Enjoy your summer.