The emerging micro-nano-processing technologies have propelled significant advances in multifunctional systems that can perform multiple functions within a small volume through integration. Herein, we present an on-chip multifunctional system based on a 1T/2H-MoS₂/graphene fishnet tube, where a micro-supercapacitor and a gas sensor are integrated. A hybrid three-dimensional stereo nanostructure, including MoS₂ nanosheets and graphene fishnet tubes, provides K⁺ ions with a short diffusion pathway and more active sites. Owing to the large layer spacing of 1T-MoS₂ promoting fast reversible diffusion, the on-chip micro-supercapacitor exhibits excellent electrochemical properties, including an areal capacitance of 0.1 F·cm^-2 (1 mV·s^-1). The variation in the conductivity of 2H-MoS₂ when ammonia molecules are adsorbed as derived from the first-principles calculations proves the Fermi level-changes theory. Driven by a micro-supercapacitor, the responsivity of the gas sensor can reach 55.7% at room temperature (27 °C). The multifunctional system demonstrates the possibility of achieving a two-dimensional integrated system for wearable devices and wireless sensor networks in the future.