An acetone gas sensor apparatus, including: a chamber, used for containing a gas sample taken from a breath of a person; and an acetone gas sensor, placed in the chamber for generating an output current in response to an acetone concentration of the gas sample, the acetone gas sensor including: a substrate; a buffer layer, deposited on the substrate; an InN epilayer, deposited on the buffer layer for providing a current path for the output current; a first conductive contact, deposited on the InN epilayer for providing a drain contact; and a second conductive contact, deposited on the InN epilayer for providing a source contact.