Does anyone know of a gastroenterologist in Samui or Phangan?

AFAIK, no, not even at Bangkok Hospital Samui.

If GI specialist is required then need to go to the mainland. The government hospital in Surat Thani is a Regional level facility and will definitely have GI specialists; may or may not have an "after hours" clinic where you can make appointments and avoid the worst of the crowds.

If you prefer private, Taksin Hospital in Surrat Thani seems to be the best of these and I would assume has at least one GI specialist.

Strange, given that there are all kinds of other specialties on the island. OK, thanks for the advice!

Strange, given that there are all kinds of other specialties on the island. OK, thanks for the advice!

Gastroenterology is a sub-specialty of General Medicine. You will find a General Physician on the island.

General physician (internal medecine) of course but he asked specifically for a GI specialist which is a defined specialty involving specialized training. Which GPs/most internists (including AFAIK all those on Samui/Phagnan) will not have had.

Whether or not he needs such a specialiat or could be adequately treated by a GP depends on the nature of the problem which was not described.

However even among specialists the level/quality is usually far better on the mainland.