A method for producing a semiconductor optical device includes the steps of forming a semiconductor layer; forming a non-silicon-containing resin layer; forming a first pattern in the non-silicon-containing resin layer; forming a silicon-containing resin layer; etching the silicon-containing resin layer to have a second pattern reverse to the first pattern; selectively etching the non-silicon-containing resin layer by a RIE method employing a gas mixture containing CF4 gas and O2 gas, the non-silicon-containing resin layer having the second pattern; and etching the semiconductor layer. In the step of selectively etching the non-silicon-containing resin layer, a side wall of the second pattern in the silicon-containing resin layer and the non-silicon-containing resin layer is formed, the silicon-containing resin layer and the non-silicon-containing resin layer are maintained at a temperature equal to or less than a freezing point of SiF4, and a protective layer containing SiF4 is formed on the side wall of the second pattern.