An oxygen sensor device is disclosed having a glass dome fluid-tightly connected at its circumferential base edge to one surface of an oxygen conductive solid electrolyte plate to form a diffusion chamber defined by the glass dome and the solid electrolyte plate. The diffusion chamber may be vacant, or may have a porous inorganic material packing layer fixedly disposed in the entire space thereof. Alternatively, the diffusion chamber may have a porous inorganic material semi-packing layer fixedly disposed in an upper portion thereof remote from the electrolyte plate, while leaving vacant the remainder of the chamber. The oxygen sensor device is advantageous from the viewpoints of miniaturization, power consumption saving and reliability.