We have demonstrated the first parallel detection of electrical signals caused by odorant responses of insect cells expressing insect odorant receptors with a 64 χ 64 complementary metal-oxide semiconductor (CMOS) monolithically integrated sensor array with surface-oxidized gate electrodes. The individual sensor element transduces odorant responses of cells contacting with each electrode into an electrical signal, which is confirmed by the corresponding fluorescence. Therefore, a high-density sensor array based on different insect OR-expressing cells could be used to make an artificial olfactory system that discriminates various odorants simultaneously, as do natural olfactory systems.