  A new combined next to leading order QCD analysis of the polarized inclusive
and semi-inclusive deep inelastic lepton-hadron scattering (DIS) data is
presented. In contrast to previous combined analyses, the $1/Q^2$ terms
(kinematic - target mass corrections, and dynamic - higher twist corrections)
in the expression for the nucleon spin structure function $g_1$ are taken into
account. The new COMPASS data are included in the analysis. The impact of the
semi-inclusive data on the polarized parton densities (PDFs) and on the higher
twist corrections is discussed. The new results for the PDFs are compared to
our (Leader, Sidorov, Stamenov) LSS'06 PDFs, obtained from the fit to the
inclusive DIS data alone, and to those obtained from the de Florian, Sassot,
Stratmann, and Vogelsang global analysis.
