Abstract Quantum well micro-Hall devices based on uniformly Si-doped Al 0.3 Ga 0.7 As/GaAs and Si-δ-doped Al 0.3 Ga 0.7 As/GaAs/In 0.3 Ga 0.7 As heterostructures are investigated as function of electric field and compared in terms of sensitivity and noise properties. The data show that at high electric fields, doped-channel quantum well devices are advantageous over high-mobility structures and that the use of pseudomorphic InGaAs results in better performance than does GaAs. A maximal signal-to-noise sensitivity (SNS) of 138 dB T −1 is achieved in a 10 μm ×10 μm device at 300 K, at frequency of 100 kHz and bandwidth of 1 Hz. This performance corresponds to a lowest detection limit of 127 nT Hz −1/2 , with no degradation for electric fields up to 2.4 kV cm −1 ; these values represent the best reported at such high electric fields. Furthermore, our results suggest that a signal-to-noise sensitivity of 160 dB T −1 and a lowest detection limit of 10 nT is achievable in doped-channel structures.