PURPOSE: To provide a semiconductor device having superior leakage current characteristics and DC current amplification factor by mesa etching the semiconductor of mesa type, and then cleaning it with a solution containing hydrogen peroxide or nitric acid.

CONSTITUTION: After an impurity is diffused in a semiconductor substrate to form a semiconductor region, a metallic layer is coated on the substrate and formed with a pattern thereat to thereby form one or more electrodes of desired shape thereon. The substrate thus formed is etched by an alkaline solution with the metallic layer as a mask, and the end of the junction surface thereof is exposed with mesa surface. Then, the exposed surface of the substrate is lightly oxidized with an oxidation liquid having a concentration of 5% of hydrogen peroxide or 0.1% of nitric acid (volumetric percentage) at 80°C. Thus, it can provide a semiconductor device which has superior leakage current characteristic and DC current amplification factor to the conventional one.