I Am Leaving My Company For Another How Do I Write The Thank You Letter?

It is an honor to be the first person to answer your question about the thank you letter.
    There is a basic format.Fist,you must state your reasons why you are ready to leave
your company to another.The invitation of friends or other reasons?what'smore,express that It is a great honor to has become part of the dynamic company and you have learned a lot about how to work in a world-famous company.Most important of all, express your gratitude to the place where you have worked.If there is a opportunity in the future,you are happy to work there.
   There  is an example.I hope it can help you.
       

XXX,   
      Hi, after serious consideration, I decided to end my work ahead of  schedule.
Maybe it is really a surprise for you, however, I need to tell you that I am seriously ill
during these days. Sorry to bring you the inconvenience.  During seven month's work in your team, I have learned a lot about how to work in a world-famous company like
Intel. Also after witnessing the whole progress that marvell purchase the whole CHG
group, I have learned the cruelty of competition in IT industry. It's obviously true that
I can still learn a lot if I continue work in your team given that I was not sick.  I will be
dedicated to hand over all my work to the responsible personnel before departure.
    Thanks again for you kindly instruction and support during my work. Wish you very success in future.    
    Best regards!    
     Sincerely