Thin-film electroluminescent (TFEL) devices have been newly developed using Y2GeO5 oxide phosphor thin films prepared by r.f. magnetron sputtering. Multicolor emissions were observed in TFEL devices fabricated using various impurity-activated Y2GeO5 phosphor thin films. A high-luminance TFEL device was fabricated using a Y2GeO5:Mn thin film prepared with a Mn content of 2 at.% and postannealed at 1020: luminances of 414 and 3020 cd/m2 and luminous efficiencies of 6.7 and 0.93 lm/W for yellow emission when driven at 60 Hz and 1 kHz, respectively. Newly developed oxide Y2GeO5:Mn phosphors are very promising for use as the thin-film emitting layer of TFEL devices.