[en] The effect of pO₂ atmosphere during annealing on electrical properties of spinel-type oxide composed of Mn, Co, and Ni used as a thermistor material was investigated. Sintered body of monophase spinel-type oxide with composition of Mn_1.5CoNi_0.5O₄ was prepared by oxidation and fired at 1400 deg C. Oxidation was conducted at 1100 deg C at which the spinel structure is stable. The spinel-type oxide was annealed in atmospheres of various pO₂ in the temperature range 100 to 300 deg C. The oxide was p-type semiconductor regardless of annealing conditions. The electrical conductivity and the mobility increased with increasing pO₂. Electrical conduction of the oxide was considered to be controlled by a small polaron hopping. Copyright (1998) Australasian Ceramic Society