We describe the use of accumulation layers of electron charge in applications as magnetoresistive devices. We consider two such systems: an InGaAs/InP heterostructure in which we identify a two‐dimensional electron gas from the observation of the quantum Hall effect, and InAs films, in which a strong surface accumulation of charge is inferred from depth profiling studies of the galvanomagnetic coefficients. Magnetoresistive devices fabricated from these materials exhibit outstanding field sensitivity and temperature stability due to the existence of electrons of relatively high density and mobility in the accumulation regions. We also model the magnetosensitivity of our devices.