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In this paper, we report on the optical characterization of a micromachined gyroscope prototype for automotive applications, by means of feedback interferometry. In order to directly detect the rotation-induced Coriolis force, we have developed a compact and stable interferometric setup, which has been positioned inside a small vacuum bell, mounted on a rotating table. By this setup, which has a noise limit of the order of 10-11 m/(Hz)12/, we have measured the gyro responsivity curve, demonstrating the feasibility of the optical interferometric detection of the in-plane response of a MEMS sensor. In addition, we have carried out the full mechanical characterization of the device at different pressures, and we have performed the matching of the gyro resonance frequencies by the interferometric monitoring. Our gyro had a resonance frequency of 3986 Hz for both axes after tuning; at a pressure of 7 10-2 torr, the quality factor were Q=18000 for the driving axis and Q=1800 for the sensing axis, while the measured responsivity was 7 10-10 m/(°/s). The optical characterization represents an important feedback to the designer and is especially powerful in the case of prototypes for which the on-board electronics is not yet available.