We study how the de transport through a semiconductor quantum dot vari
es when time-dependent external fields are applied. We find (i) the sh
ift of the Coulomb blockade region due to the interband excitation, (i
i) the resonant peak structures of the Coulomb oscillation due to the
intraband excitation, and (iii) the electron pumping effect in the qua
ntum dot modulated by the microwave field with frequency lower than th
e level spacing of the quantum dot.