In this work, we demonstrate a selective gas sensor based on monitoring two different detection mechanisms; absorption and thermal conductivity. To illustrate the concept, we utilize a resonator composed of a clamped-guided arch beam connected to flexural beams and a T-shaped moveable mass. The resonator has two distinct out-of-plane modes in which the mass motion dominates the first mode while the motion of the flexural beam dominates the second mode. A highly disperse graphene oxide (GO) solution is prepared and drop-casted over the moveable mass structure using the inkjet printer for humidity sensing. On the other hand, the He is detected using the hot flexural beams. The results show no significant effect of humidity on the flexural mode (FM) nor for He on the mass mode (MM). This indicates a new technique for selectivity and identification. The device shows good sensitivity (50.1% to 50% RH @ MM and 39.2% to 50% He @ FM: (Vac = 1.5V)), linearity, and repeatability with excellent selectivity. It is demonstrated that the FM has great potential for detecting and categorizing different gases according to their thermal conductivity. The demonstrated multimode MEMS resonator can be a promising approach for the development of smart, highly selective, and sensitive gas/chemical sensors.