The gallium arsenide single crystal substrate has a circular main surface, and when the diameter of the main surface of the gallium arsenide single crystal substrate is represented by D and the number of etch pits formed on the main surface by immersing the gallium arsenide single crystal substrate in molten potassium hydroxide at 500° C. for 10 minutes is counted, the number C1 of etch pits in a first circular region having a diameter of 0.2D around the center of the main surface is 0 or more and 10 or less.