Electrical characterizations of the first n–N HgCdTe heterojunctions grown in situ by molecular‐beam epitaxy are reported. The cadmium concentrations of the two materials are 0.18 for the bottom layer and 0.26 for the top. The measurements by Hall, IV, CV, and spectral responsivity are consistent with the existence of a conduction‐band barrier at the interface behaving as an insulator at low temperature. We suggest that transient effusion cell fluxes occurring during shutter sequencing created such barriers at the heterojunction interfaces during the growth. The high R0A (600 Ω×cm2) measured suggests that this effect might be of interest for future heterojunction gate field‐effect transistor investigations.