What visa should I apply for to live and possibly teach in Chiang Mai, Thailand for 6-9 months?

Have you looked at the pay? Most government schools pay 25-30,000 Baht a month. Less than $1,000 USD. Some private schools pay more, some around 60,000 baht, especially in Phuket.

Either get a single entry (60-day) tourist visa or fly in and take the 30-day no-visa entry. Either of them can be extended for another 30 days.

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Once you are here you can decide what you want to do.

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You can work on-line and stay as a tourist (6 months to 1 year without a problem) or you can find a classroom job and change to a non-B visa and work permit.

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If you are hoping to get a regular classroom job then bring your original degree, transcripts, a state or FBI check and an open mind (this isn't the same as home).

If you don't have a degree then you won't be getting a work permit. Join the rest of the digital nomads in CM.

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Try the site and see if you can get a teaching job before you arrive

Keep in mind the thai consulates in the US that sell the 6 month METV require a bank statement with $7000 USD in your account.

if you can't meet that requirement just get a single entry tourist visa before you come here.

You can always apply for a student visa and then look for work that way, then once found cancel the ed visa and get the Non-O....the ed visa will give you the 6-9 months you’re looking for in country without having to leave every 30-60 days...

The 6 month METV is sold in the following thai consulates in the US;

Chicago, Los Angeles, New York & Washington DC.

Did you look at any of those websites?

youy cant work on a tourist visa