Resonant tunneling wells with approximately V-shaped profiles have been fabricated by '-doping AlxGa1-xAs tunnel barriers. The structures show strong resonances in their current-voltage characteristics in qualitative agreement with the expected subband structure. Magnetotunneling experiments are shown to measure the electron density in the lowest subband which displays a strong asymmetry as a function of the bias voltage. This is indicative of an extremely asymmetric electric field distribution within the structure and is explained by a consideration of the dynamics of the electrons tunneling into, or out of, a slightly asymmetric well. The implications for asymmetries in other semiconductor structures are pointed out. © 1989 The American Physical Society.