The present disclosure provides a gas sensor including: a substrate; an electrode formed on the substrate; and a gas-sensing layer formed on the electrode, wherein the gas-sensing layer is a self-heating nanocolumnar structure having nanocolumns formed on the electrode and inclined with respect to the electrode with an angle of 60-89° and gas diffusion pores formed between the nanocolumns. The gas sensor according to the present disclosure requires no additional heater since it self-heats owing to the nanocolumnar structure and exhibits superior gas sensitivity even when no heat is applied from outside. Also, it can be mounted on mobile devices such as mobile phones because it consumes less power.