PURPOSE: To protect an electrode on the upper part of a mesa structure against disconnection or to prevent it from increasing in resistance by a method wherein a part of the electrode is brought into contact with the upside periphery of the mesa structure overriding a rugged edge line.

CONSTITUTION: An insulating layer 12 is made to extend to the upper peripheral part of a mesa structure 16, an edge line in contact with the peripheral part is formed rugged, and an electrode 17 is formed on the insulating layer 12. Moreover, a part of the electrode 17 is brought into contact with the upside periphery of the mesa structure 16 overriding the rugged edge line. The edge line of the insulating layer 12 is formed rugged on the upper part of the mesa structure 16, and the electrode 17 formed on the insulating layer 12 is brought into contact with the peripheral part of the mesa structure overriding the rugged edge line concerned, so that a boundary line along the rugged edge line between a part of the electrode 17 on the insulating layer 12 and another part of the electrode 17 on the mesa structure 16 becomes large in length. By this setup, an electrode is hardly disconnected at a boundary line, and even if a part of the electrode is disconnected, the electrode has a function enough to conduct electricity as a whole, so that the electrode can be protected against disconnection and prevented from increasing in resistance.