In how many semesters can a MS degree in US be completed ?

I just want to ask that a MS degree from US spans two or three semesters. I was browsing some websites for probable tuition fee, they don’t show it as lumpsum but on a per semester basis. As I have to do a comparitive analysis of the affordability of differenent universities,so can anyone please make the whole semester thing clear to me ?

P.S. If possible I alse need to be enlightened about the credits and working hours.They are too confusing to start with.