  We present a next-to-leading order (NLO) computation of the full set of
polarized and unpolarized electroweak semi-inclusive DIS (SIDIS) structure
functions, whose knowledge is crucial for a precise extraction of polarized
parton distributions. We focus on the phenomenology of the polarized structure
functions for the kinematical conditions that could be reached in an
Electron-Ion-Collider.
  We show that the NLO corrections are sizeable, particularly in the small-$x$
range. We test the sensitivity of these structure functions on certain quark
distributions and compare it to the situation of inclusive DIS and
electromagnetic SIDIS.
