Metal oxide semiconductor (MOS) based gas sensors for triethylamine (TEA) are anticipated with low operating temperature, high response, and robust manufacturing process. TEA sensors with the α-Fe₂O₃@NiO or α-Fe₂O₃@CuO core-shell nanorods (NRs) heterostructure are successfully fabricated and their sensing performance is optimized by controlling the shell thickness based on Debye length. Porous α-Fe₂O₃ NRs are directly prepared on flat Al₂O₃ substrates by convenient hydrothermal process. The p-type shell layer is deposited by pulsed laser deposition (PLD) method, which width is controlled by changing the applied laser pulses. Due to the formation of PN heterojunction, the core-shell NR heterostructures show enhanced performances than pristine α-Fe₂O₃ NRs at near room-temperature, e.g. 40 °C. Moreover, such heterostructural sensor performances also exhibit a strong dependence on the shell thickness. When the p-type shell thickness is close to its Debye length (λ_d), the core-shell sensor of the highest response is realized. The enhanced sensing properties of this core-shell NR heterostructure toward TEA can be explained by the increase of initial resistance (R_a) due to the modulation of depletion layer through optimizing the p-type shell thickness.