Thailand’s economy has developed strongly by consistently attracting foreign investment especially since the 1980s, despite political upheavals and persistent corruption amidst ongoing challenges. It has also expanded the numbers and scope of its investment treaties, including more options for investor–state dispute settlement arbitrations to enforce substantive commitments to foreign investors, resulting in a few treaty-based arbitrations as well as some contract-based arbitrations involving foreign investors. A few, and possibly the Kingsgate v. Thailand claim under the Thailand–Australia Free Trade Agreement since 2017, have involved allegations and investigations concerning corruption and other serious illegal behaviour. As reiterated in the conclusion, corruption investigations and court proceedings are necessarily very lengthy, sometimes more so than the time taken to generate and enforce final awards in large (especially treaty-based) investment arbitrations. To reduce the consequent risk of enforcing an award that later proves to be based on seriously corrupt conduct, one solution may be for investment treaty arbitrators to apply the same higher standard of proof that corruption investigators and criminal courts need to apply, although this will mean more delays and perhaps costs in arbitration. Secondly, more transparency could be added to Thailand-related investment arbitration proceedings, so that the public at least knows that corruption is being alleged.