A new etchant for GaAs consisting of CrO3, HF, AgNO3, and H2O is described which selectively attacks dislocations on the following planes: Ga {111}, As {111}, {100}, and {110}. Dislocations normal, inclined, and parallel to the plane of observation are revealed. The etching figures were correlated with dislocations by equating (a) the etch pits produced on {111} surfaces with those produced by a known dislocation etchant, (b) the {111} etch pits with the linear structure appearing on {100}, and (c) the pits on two matched {110} cleavage planes. Supporting evidence obtained from plastic indentation experiments on {111} and {100} is also presented. It is observed that long, straight dislocations tend to lie in ⟨110⟩ and ⟨112⟩ directions. It was established by reverse bending experiments that the etchant produces pits only at As or &bgr; dislocations, if no impurity segregation has occurred. If decoration of the dislocations has occurred, as in Bridgman‐grown GaAs, pits are produced at both &agr; (Ga) and &bgr; dislocations.The relative etching rates for the {100}, Ga {111}, {110}, and As {111} faces are 1.0, 0.71, 0.69, and 0.50, respectively.Stacking faults on {100} are also revealed by the etchant on epitaxial films. A second etchant is reported which reveals stacking faults on the As {111} faces of GaAs. This etchant is the same as the dislocation etchant but with the CrO3absent.