Provided herein is a gas sensor apparatus including a first sensor unit, second sensor unit, and signal processing unit. The first sensor unit has a channel area doped to an n-type such that it may selectively react to a donor molecule in gas. The second sensor unit has a channel area doped to a p-type such that it may selectively react to an acceptor molecule in gas. The signal processing unit receives a sense signal of the donor molecule from the first sensor unit and a sense signal of the acceptor molecule from the second sensor unit, processes the received sense signals and generates result data of processing the received sense signals. Therefore, the gas sensor apparatus may selectively sense donor gas and acceptor gas.