The flavor asymmetry of the light quark sea of the nucleon is determined in
the kinematic range 0.02 < x < 0.3 and 1 < Q(2) < 10 GeV2 for the first ti
me from semi-inclusive deep-inelastic scattering. The quantity [(d) over ba
r(x) - (u) over bar(x)]/[u(x) - d(x)] is derived from a relationship betwee
n the yields of positive and negative pions from unpolarized hydrogen and d
euterium targets. The flavor asymmetry (d) over bar - (u) over bar is found
to be nonzero and x dependent, showing an excess of (d) over bar over (u)
over bar quarks in the proton.