Diamond semiconductor element and process for producing the same

A process for producing a diamond semiconductor, characterized by comprising a first process-step of implanting dopant into a diamond by an ion implantation technique, a second process-step of forming a protective layer on at least part of the surface of said ion-implanted diamond, and a third process-step of firing said ion-implanted diamond protected by said protective layer under a pressure of no less than 3.5GPa and at a temperature of no less than 600°C is disclosed.