Abstract: A field effect gas sensor, for detecting a presence of a gaseous substance in a gas mixture, the field effect gas sensor comprising: a SiC semiconductor structure; an electron insulating layer covering a first portion of the SiC semiconductor structure; a first contact structure at least partly separated from the SiC semiconductor structure by the electron insulating layer; and a second contact structure conductively connected to a second portion of the SiC semiconductor structure, wherein at least one of the electron insulating layer and the first contact structure is configured to interact with the gaseous substance to change an electrical property of the SiC semiconductor structure; and wherein the second contact structure comprises: an ohmic contact layer in direct contact with the second portion of the SiC semiconductor structure; and a barrier layer formed by an electrically conducting mid-transition-metal oxide covering the ohmic contact layer.