It is to provide a thermodynamically and chemically stable dopant material which can achieve controls of the pn conduction types, carrier density, and threshold value of gate voltage, and a manufacturing method thereof. Further, it is to provide an actually operable semiconductor device such as a transistor with an excellent high-speed operability and high-integration characteristic. Provided is a dopant material obtained by depositing, on a carbon nanotube, a donor with a smaller ionization potential than an intrinsic work function of the carbon nanotube or an acceptor with a larger electron affinity than the intrinsic work function of the carbon nanotube. The ionization potential of the donor in vacuum is desired to be 6.4 eV or less, and the electron affinity of the acceptor in vacuum to be 2.3 eV or more.