A method for producing a semiconductor substrate includes the steps of: forming a first patterned mask containing a material having a growth suppressing effect on a substrate; growing a first nitride semiconductor on a portion of the substrate corresponding to an opening portion of the first patterned mask; forming a second patterned mask containing a material having a growth suppressing effect only on a main surface of the first nitride semiconductor which is positioned above the opening portion of the first patterned mask; and growing a semiconductor crystal substantially from the side surface of the first nitride semiconductor so as to form a second nitride semiconductor which integrally includes the first patterned mask and the second patterned mask.