A chemical etching orientation method is suggested for the ZnGeP2 crystals. Several polished faces of ZnGeP2 crystals were etched in a certain etching solution. Some regular etch pits appeared on all samples. The indices of side facets of the etch pits were measured by X-ray rocking method, which mainly belong to {204}, {112} and {110}. Then the three crystallographic axes of the crystals were determined according to the angle relationship. Finally, optical parametric oscillator (OPO) devices were cut at the direction of theta=0 degrees and phi=53 degrees. (C) 2010 Elsevier B.V. All rights reserved.