  Polarised Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes allow to
study Transverse Momentum Dependent partonic distributions (TMDs), which reveal
a non trivial three dimensional internal structure of the hadrons in momentum
space. One of the most representative of the TMDs is the so-called Sivers
function that describes the distribution of unpolarized quarks inside a
transversely polarized proton. We present a novel extraction of the Sivers
distribution functions from the most recent experimental data of HERMES and
COMPASS experiments. Using suitable parametrizations, within the TMD
factorization scheme, and a simple fitting strategy, we also perform a
preliminary exploration of the role of the proton sea quarks.
