An asymmetric artificial scatterer in a semiconductor microjunction is shown to dramatically affect the nonlinear transport of ballistic electrons. The chosen device geometry, defined in a GaAs-AlGaAs heterostructure, successfully guides carriers in a predetermined spatial direction, independent of the direction of the input current I. From the nonlinear current-voltage characteristic we obtain unusual symmetry relations for the four-terminal resistances with Rij,kl(I)≈-Rij,kl(-I) and Rij,kl(B)≫Rkl,ij(-B) even at zero magnetic field B. The ballistic rectifier thus realized relies on a new kind of rectification mechanism entirely different from that of an ordinary diode.