COMPOUND SEMICONDUCTOR SUBSTRATE AND POWER AMPLIFICATION MODULE

PROBLEM TO BE SOLVED: To provide a compound semiconductor substrate improving peeling resistance.SOLUTION: A compound semiconductor substrate has a first principal surface parallel with a first direction and a second direction orthogonal to the first direction, a second principal surface facing the first principal surface, and a recess forward from the first principal surface toward the second principal surface. The recess has an opening formed in the first principal surface, a bottom face facing the opening, and multiple lateral faces forming a recess between the opening and the bottom face. The multiple lateral faces include at least one first lateral face extending in the first direction, and forming an angle of about θ (0