A method of manufacturing a semiconductor device including a substrate; a first nitride layer containing gallium on the substrate; and a second nitride layer containing silicon on the first nitride layer includes generating an etchant of a gas containing chlorine atoms or bromine atoms; and selectively removing the second nitride layer, wherein the etchant is generated by plasma discharge of the gas, wherein the second nitride layer and the first nitride layer are prevented from being irradiated with ultraviolet rays generated at a time of the plasma discharge, and wherein the selectively removing the second nitride layer includes etching the second nitride layer under a first atmosphere at a first pressure that is lower than a first saturated vapor pressure of a silicon compound and that is higher than a second saturated vapor pressure of a gallium compound.