Dear Professor Lee,
I am the the representative of the students' union from XXX University. I am writing to you in the honor of our students' union to invite you to give a lecture on the development of software. We've heard of your reputation for a long time and know you are an expert in this field. If you can give a lecture in our university we will be excited to see you by our own eyes.
If you decide to be here,please let us know as soon as possible.We are looking forward to getting your reply soon.
Best Regards
Students' Union of XXX University