To improve the measurement precision of a disposable biosensor, we have developed a multi-working electrode biosensor with a differential format using thick film technology. Each output signal of three active working electrodes controlled with a multi-channel potentiostat produced a corresponding differential signal relative to a common inactive working electrode and the final output signal was an average of three differential signals. As a model analyte, ethanol vapor was chosen. The results clearly established the superiority in reproducibility of the multi-working electrode biosensor with a differential format to the simple differential-type biosensor with an active working electrode.