  We study the single spin asymmetry (SSA) for the pion production with large
transverse momentum p_T in semi-inclusive deep inelastic scattering
$ep^\uparrow\to e\pi X$. We derive the twist-3 cross section formula for SSA,
focussing on the soft-gluon-pole contributions associated with the twist-3
distribution for the nucleon and with the twist-3 fragmentation function for
the pion. We present a simple estimate of the asymmetries due to each twist-3
effect from nucleon and pion, respectively, by fixing the overall strength of
the relevant nonperturbative quantities by the data on the SSA A_N in
$p^\uparrow p\to\pi X$ collision.
