Heterojunctions of solid C70 andn‐ orp‐type crystalline Si have been made. Current–voltage measurements show that both C70/n‐Si and C70/p‐Si contacts are rectifying but their directions of rectification are opposite to each other. Thermal activation measurements at a fixed forward bias show an exponential dependence of current on the reciprocal of temperature, from which we determine the effective barrier height as 0.23 eV for C70/n‐Si and 0.27 eV for C70/p‐Si. Relative dielectric constant of solid C70 was determined to be 4.96 through the study of high‐frequency capacitance–voltage characteristics for Ti/C70/p‐Si structures. ©1995 American Institute of Physics.