PURPOSE: To provide a manufacture of a semiconductor device wherein breakdown can be made hard to occur and electric property can be improved by preventing the concentration of an electric force line at the pn junction interface edge made by diffusion, without performing the formation of a guard ring by ion implantation.

CONSTITUTION: This is constituted to include a process of forming an InGaAs crystal layer 6 having a thick part and a thin part on an InP crystal layer 1 and a process of diffusing dopant into the InP crystal layer 1 through the InGaAs crystal layer 6 and forming a diffused layer 2 by heat-treating it in dopant atmosphere.