Praweenwat Boonyong scored the winning goal with a penalty kick in the 23rd minute. The Thais will meet Indonesia in tomorrow's final.
Indonesia upset defending champions Malaysia 4-3 on penalties after a 1-1 draw in yesterday's other semi-final.
Thailand will be heavy favourites against Indonesia who lost 4-1 to the Thais earlier in the Myanmar Games.
Thailand are bidding to regain the title they won eight times in a row until 2007. They were eliminated in the first round in the previous two tournaments in 2009 and 2011.