A method for manufacturing a surface emitting type AlGaAs/GaAs semiconductor LASER diode by a selective epitaxy method which is capable of forming naturally a 45.degree. mirror reflective face during the epitaxy method itself. The method comprises the steps of forming a silicon oxide or silicon nitride layer on one side of a n-type single crystal GaAs substrate as a mask, removing the mask of the regions each for forming a 45.degree. mirror reflective face and a LASER diode by use of a photolithography and a chemicaletching, forming the two layers by removing the photoresistor on the remaining mask after a selective epitaxy process and converting a slant face of the LASER diode into a vertical face, depositing a n-type metal layer on the other side of the substrate, and carrying out a heat treatment.