Ethmia chemsaki is a moth in the Depressariidae family. It is found from Puebla, Mexico to northern Costa Rica, where it has been collected on the Pacific slope of Cordillera de Guanacaste at altitudes ranging from 20 to 300 meters. The length of the forewings is 8-9.2 mm. The ground color of the forewings is white, with black markings, faintly reflecting metallic blue. The ground color of the hindwings is white, becoming brown toward the apical margin. Adults are on wing in June.