A compound semiconductor device includes a laminated body including a crystal substrate and a compound semiconductor multilayer film. The laminated body has a major surface, a first side face, a second side face, a third side face, and a fourth side face. The first and the second side faces are opposed to each other, substantially perpendicular to the major surface of the laminated body, made of cleaved surfaces. The third and the fourth side faces are perpendicular to the major surface and to the first and the second side faces, opposed to each other, and made of uncleaved surfaces. A groove is provided on the third side face, and the groove has a depth varied with position as viewed from the major surface, and has ends not reaching the first and second side face.