A method of producing an indium phosphide substrate; the indium phosphide substrate comprising a main surface for forming an epitaxial crystal layer and a back surface opposite to the main surface, wherein the back surface has a SORI value of 2.5 μm or less, as measured with the back surface of the indium phosphide substrate facing upward; the method comprising the steps of: cutting a wafer from an indium phosphide ingot with a wire saw; etching the cut wafer; chamfering an outer peripheral portion of the wafer after the etching; polishing at least one surface of the chamfered wafer; and etching the polished wafer, wherein the step of cutting the wafer from the indium phosphide ingot with the wire saw comprises a step of constantly delivering a new wire while reciprocating the wire in a horizontal direction, and moving a stage on which the indium phosphide ingot is placed in a vertical direction toward the wire, wherein a new wire delivering rate of the wire is from 10 to 60 m/min, a reciprocating rate of the wire is from 300 to 350 m/min, a vertical moving rate of the stage on which the indium phosphide ingot is placed is from 200 to 400 μm/min, and abrasive grains of the wire saw have a viscosity of from 300 to 400 mPa·s, wherein the step of etching the cut wafer comprises etching the cut wafer by a total of 5 to 15 μm from both sides, and wherein the step of etching the polished wafer comprises etching the polished wafer by a total of 8 to 15 μm from both sides. the indium phosphide substrate comprising a main surface for forming an epitaxial crystal layer and a back surface opposite to the main surface, wherein the back surface has a SORI value of 2.5 μm or less, as measured with the back surface of the indium phosphide substrate facing upward; the method comprising the steps of: cutting a wafer from an indium phosphide ingot with a wire saw; etching the cut wafer; chamfering an outer peripheral portion of the wafer after the etching; polishing at least one surface of the chamfered wafer; and etching the polished wafer, wherein the step of cutting the wafer from the indium phosphide ingot with the wire saw comprises a step of constantly delivering a new wire while reciprocating the wire in a horizontal direction, and moving a stage on which the indium phosphide ingot is placed in a vertical direction toward the wire, wherein a new wire delivering rate of the wire is from 10 to 60 m/min, a reciprocating rate of the wire is from 300 to 350 m/min, a vertical moving rate of the stage on which the indium phosphide ingot is placed is from 200 to 400 μm/min, and abrasive grains of the wire saw have a viscosity of from 300 to 400 mPa·s, wherein the step of etching the cut wafer comprises etching the cut wafer by a total of 5 to 15 μm from both sides, and wherein the step of etching the polished wafer comprises etching the polished wafer by a total of 8 to 15 μm from both sides. cutting a wafer from an indium phosphide ingot with a wire saw; etching the cut wafer; chamfering an outer peripheral portion of the wafer after the etching; polishing at least one surface of the chamfered wafer; and etching the polished wafer, wherein the step of cutting the wafer from the indium phosphide ingot with the wire saw comprises a step of constantly delivering a new wire while reciprocating the wire in a horizontal direction, and moving a stage on which the indium phosphide ingot is placed in a vertical direction toward the wire, wherein a new wire delivering rate of the wire is from 10 to 60 m/min, a reciprocating rate of the wire is from 300 to 350 m/min, a vertical moving rate of the stage on which the indium phosphide ingot is placed is from 200 to 400 μm/min, and abrasive grains of the wire saw have a viscosity of from 300 to 400 mPa·s, wherein the step of etching the cut wafer comprises etching the cut wafer by a total of 5 to 15 μm from both sides, and wherein the step of etching the polished wafer comprises etching the polished wafer by a total of 8 to 15 μm from both sides.