Dear …
Please accept my warmest thanks for sponsoring me for the __(type of Scholarship)__. What an amazing honor it is to have be offered this Scholarship. I am so happy that you gave me __(the opportunity/your support/etc.)__ to achieve this goal. I have worked very hard work for an opportunity like this, yet I know that I could not have done without your sponsorship and I just want to personally tell you how very grateful I am to you.
It has been a real pleasure __(working with/studying under/etc)__ and I will always treasure the memories I have of it. I am now looking forward to __(briefly describe what your next steps will be)__. This new path for me is all so exciting and yet a little bit scary at the same time. Still, with all it has to offer, I am ready to embrace it all!
Once again, thank you so much for your sponsorship. I am truly grateful.
Sincerely,