Cognomen Thammachai (ธรรมชัย 
, ธรรมไชย , Thammachai 
) , across the world, is quite a rare family name. The family name Thammachai is habitual in South-eastern Asia, particularly Thailand, where it is quite a rare surname. Much less frequently, Thammachai is the forename as well as the last name.
Lai, Pakamas, Prasert, Preecha, Phunpikul, Rangsan, Rujirek, Gaywarin, Narawan, Nonglak, Orathai, Yathida, Maneerat, Siriporn, Suradech, Anchalee, Chanchai, Chankham, Chanjira, Benjamas, Kanchana, Kwanchai, Panatda, Bhimmawajna, Chaiwat, Ajchamon, Tom, Malee, Suwan, Vasin, Orasa, Monton, Somjai, Arissa, Apisek, Deriya, Patiphon, Dakham, Thanat, Nischa, Onrunchana, Yadapa, Mongkon, Saisuda, Sinthai, Sommitch, Somphon, Somchat, Jidapa, and Panichar