An epitaxial thin-film capacitor based on relaxor ferroelectric oxide, BaTiO3-Bi(Mg2/3Nb1/3)O-3 ( BT-BMN), has been realized on Nb:SrTiO3 substrates. A high dielectric constant exceeding 400 was attained on high-temperature annealed films at frequencies below 100 kHz. BT-BMN thin-film exhibited a broad dielectric constant variation against temperature and also the frequency dependent dielectric-constant-maximum temperature. Excellent dielectric constant stability below 10% was achieved in 75-400 degrees C temperature range with a low dielectric loss. This exemplifies BT-BMN as a dielectric for monolithically integrated capacitors that can function up to 400 degrees C, breaking the present 175 degrees C limit of bulky capacitors, in high-power high-temperature electronic devices. (C) 2015 Elsevier B.V. All rights reserved.