It was recently shown that Shubnikov–de Haas (SdH) oscillations observed in conventional resistance measurements can be dramatically enhanced by light‐induced carrier modulation [S. E. Schacham, E. J. Haugland, and S. A. Alterovitz, Appl. Phys. Lett. 61, 551 (1992)]. Here we report on a similar observation in the case of contact‐free, microwave‐detected SdH oscillations. In the original version of this nondestructive technique [P. Omling, B. Meyer, and P. Emanuelsson, Appl. Phys. Lett. 58, 931 (1991)], magnetic‐field modulation was applied in order to enhance the sensitivity. If, instead, the carrier concentration is modulated by illumination, we show that a similar enhancement in the sensitivity of the signal is obtained. We demonstrate that very simple microwave equipment can be used for the measurements, and that the accessible magnetic‐field region can be extended, allowing for contact‐free transport investigations in the high magnetic‐field region.