  AMS-02 is a high precision magnetic spectrometer for cosmic rays in the GeV
to TeV energy range. Its tracker consists of nine layers of double-sided
silicon microstrip sensors. They are used to locate the trajectories of cosmic
rays in the 0.14 T field of a cylindrical magnet, thus measuring their rigidity
$p/Z$ and charge sign. In addition, they deliver a high resolution measurement
of the absolute charge $|Z|$. The detector has been designed to operate in
space with a position resolution of about 10 $\mu$m for each hit and charge
identification capabilities up to $Z=26$. In this talk I describe the
performance in orbit of this detector component and its impact on the overall
performance of the spectrometer.
