@Ch***
&
@Kel***
keep in mind that the STV (Special Tourist Visa) is valid for 3 months from the date you get it <-meaning you have that long to ENTER thailand on it. When you enter the country you get stamped in for 90 days. You can apply for 2 additional extensions of 90 days each at the immigration office BUT you CANNOT change that visa to any other type inside the country.
It's sold as a tourist visa <- meaning you come here, "tour" for 9 months then leave and go back to where ever it is you come from