Electronic properties of the major and minor isomers of Pr@C-82, I (C-2nu,) and 11 (C,), are studied by Raman scattering, resistivity measurement, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The valences of the Pr atom in both isomers are determined to be +3 based on the Raman shift in the Pr-C-82 stretching mode. The transport properties showed that both isomers are normal semiconductors with a small energy gap (E-g). STM of isomer I shows internal structures dependent on bias voltage V-s, and STS shows that this isomer is a semiconductor with E-g = 0.7 eV. (C) 2004 Elsevier B.V. All rights reserved.