A semiconductor substrate according to the present invention includes a nitride semiconductor layer 203, an amorphous semiconductor layer 205 formed on one main surface side of the nitride semiconductor layer 203, a high-roughness layer 206 which is a semiconductor layer formed on the amorphous semiconductor layer 205 and has a surface roughness larger than the amorphous semiconductor layer 205, and a diamond layer 207 formed on the high-roughness layer 206. Damage to the nitride semiconductor layer can be reduced in forming the diamond layer on the nitride semiconductor layer and adhesion between the layers can be increased.
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