An InAs thin film formed by epitaxial growth on an insulating or semi-insulating substrate has a structure in which a portion near the interface of the InAs thin film with the substrate is a lower electron mobility portion, and another portion more remote from that interface is a higher electron mobility portion. The thin film is doped with donor impurity atoms in at least the high mobility portion. A magnetoelectric transducer has the InAs thin film as a magneto-sensitive portion. A magnetic amplifying type magnetoelectric transducer has a body of a ferromagnetic material arranged in the vicinity of the magneto-sensitive portion.