A decoupled-sense-mode z-axis micromachined gyroscope is presented. The sense mode is restricted to be only one degree of freedom for vibration, which restrains the effect from the drive mode and reduces the undesired sense mode bias. Using double masses allows both matched natural frequencies and decoupled modes. A U-shaped beam is utilized for meeting the requirements on the degrees-of-freedom of the drive and sense modes. In order to create a high-aspect ratio structure, a Deep Reactive Ion Etching (DRIE) process is used to achieve a larger proof mass, reduce the thermomechanical noise floor and provide high sensitivity. The area of the fabricated gyroscope is 2 100 μm×2 100 μm, with a thickness of 60 μm. The gyroscope is vacuum-packaged for a high mechanical quality factor. Measured results show that the drive and sense mode quality factors are 2 000 and 1 800, respectively, and the thermomechanical noise floor is 3.76 ( °)/h·Hz-12. The scale factor is 21 mV/(°)·s-1 in a range of ±200 (°)/s, with a full-scale nonlinearity of 1.426 %FS. The bias drift is 0.057 9 (°)/s over a 1 h measurement period.