Dear Professor (或者 Dear Dr.),

I am writing to express my heartfelt gratitude to you for the excellent guidance that you provided me during my studies at this university. Your dedication, encouragement and support were instrumental in shaping my future and helping me achieve my academic and personal goals.
Your high standards of teaching and your commitment to academic excellence have left a lasting impression on me. Your classes were always thought-provoking, engaging and challenging, and I appreciated the opportunity to learn from you. Your willingness to go above and beyond to help me with my studies was truly remarkable, and I cannot thank you enough for your invaluable guidance.
Beyond your academic support, you also helped me navigate the complexities of university life, offering me invaluable personal advice and encouragement. You showed a genuine interest in my well-being and always took the time to listen to me and offer your support. Your unwavering kindness and care left me with a deep sense of respect and admiration for you.
As I prepare to move on to the next chapter of my life, I will always carry with me the lessons that you taught me, and the admirable qualities that you embody. You have not only taught me important academic knowledge, but also valuable life lessons that will continue to guide me on my journey.
In closing, I want to once again express my sincere gratitude for everything that you have done for me. You have truly made a difference in my life and touched me in a way that will stay with me forever.
Thank you again for everything.
Sincerely,
(Your name)