For example, a four-component metal oxide such as an In???Sn???Ga???Zn???O-based oxide semiconductor, a three-component metal oxide such as an In???Ga???Zn???O-based oxide semiconductor, an In???Sn???Zn???O-based oxide semiconductor, an In???Al???Zn???O-based oxide semiconductor, a Sn???Ga???Zn???O-based oxide semiconductor, an Al???Ga???Zn???O-based oxide semiconductor, or a Sn???Al???Zn???O-base