Last name เพชรโกศัย (Petchkosai 
, เพชรโกศัย , Petchgosai ) , in the world, is a very rare cognomen. The cognomen เพชรโกศัย is habitual in South-eastern Asia, particularly Thailand, where it is a very rare surname. Much less frequently, เพชรโกศัย is the forename as well as the last name.