  We derive mass corrections for semi-inclusive deep inelastic scattering of
leptons from nucleons using a collinear factorization framework which
incorporates the initial state mass of the target nucleon and the final state
mass of the produced hadron. The formalism is constructed specifically to
ensure that physical kinematic thresholds for the semi-inclusive process are
explicitly respected. A systematic study of the kinematic dependencies of the
mass corrections to semi-inclusive cross sections reveals that these are even
larger than for inclusive structure functions, especially at very small and
very large hadron momentum fractions. The hadron mass corrections compete with
the experimental uncertainties at kinematics typical of current facilities, and
will be important to efforts at extracting parton distributions or
fragmentation functions from semi-inclusive processes at intermediate energies.
