In a semiconductor device, the degree of flatness of 0.3 nm or less in terms of a peak-to-valley (P-V) value is realized by rinsing a silicon surface with hydrogen-added ultrapure water in a light-screened state and in a nitrogen atmosphere and a contact resistance of 10−11 Ωcm2 or less is realized by setting a work function difference of 0.2 eV or less between an electrode and the silicon. Thus, the semiconductor device can operate on a frequency of 10 GHz or higher.