In this study, nanometer-scale scratch experiments were performed with a gallium arsenide (GaAs) semiconductor using an atomic force microscope (AFM) driving mechanism with a high-rigidity diamond tip cantilever. The relationship between the crystal orientation of the GaAs and the crack generation mechanism was examined by changing the scratching direction for GaAs(100) wafer. It was found that micro-crack could easily be formed in both the [011] and [0[‾1]1] directions, and the machining-induced affected layer in the [011] direction was thicker than those in the other directions. A scratch simulation confirmed the generation of cracks inside the sample in both the [011] and [0[‾1]1] directions. The depth of the crack propagation in the [011] direction was deeper than the depths in the other directions.