High-luminance multicolor-emitting thin-film electroluminescent (TFEL) devices have been developed using a new Mn- and Cr-co-doped Ga2O3 phosphor with variations of both Mn and Cr from 0 to a content of 20 at. %. Ga2O3:Mn,Cr TEEL devices driven at 1 kHz exhibited a change from green to red in emission color, maintaining luminances above 100 cd/m(2), when the co-doped Cr content was varied from 0 to 20 at. % under a constant Mn content of 0.3 at. % doping. In addition, the emission color of a Ga2O3:Mn,Cr TEEL device co-doped with a Mn content of 0.3 at. % and a Cr content of 3 at. % changed from green to red with an increase of the applied voltage.