A semiconductor substrate according to one embodiment includes: a first transistor having a first gate insulating film formed on a semiconductor substrate, a first gate electrode formed on the first gate insulating film and a first sidewall formed on a side face of the first gate electrode, the first gate insulating film comprising a high-dielectric constant material as a base material, a part of the first sidewall contacting with the first gate insulating film and containing Si and N; and a second transistor having a second gate insulating film formed on the semiconductor substrate, a second gate electrode formed on the second gate insulating film and a second sidewall formed on a side face of the second gate electrode so as to contact with the second gate insulating film, the second gate insulating film comprising a high-dielectric constant material as a base material, a part of the second sidewall contacting with the second gate insulating film and containing Si and N, wherein at least one of an abundance ratio of Si—H bond to N—H bond per unit volume, an amount of Cl per unit volume and an amount of H per unit volume of the second sidewall is larger than that of the first sidewall; and a threshold voltage of the second transistor is higher than that of the first transistor.